Lots of good advice above and im going to echo some of it but honestly the majority of this is going to be tough love whether you like it or not and I mean it with the utmost respect.
To Start, My chick and I have been exactly where you are. Two and a half years ago we were both overweight, out of shape and eating like crap every single day. (I am 5'7" and weighed 170lbs. I hover around 135 now)
How did we fix it? We changed our diet and started exercising. Pretty crazy right? One of my favorite questions I get asked by people I haven't seen in a while is "OMG You lost so much weight!?!? How did you do it????" My response, I started eating healthy and exercising 6 days a week.... they are always somehow shocked by this response, "oh..." ughh yeah, hate to break it to you but there are no short cuts and not magic bullets with this one. If you want it you have to earn it.
Yes its hard, you will be sore, your are going to crave junk food and I still do now. But if you are are serious about wanting to get in shape you have to quit being lazy and stop making excuses and just do it. NO ONE can do it for you, it is hard, it is work but only you can do it. I tell people there are plenty of days I come home after spending 12+ hours at two jobs and I still exercise and eat a healthy meal before KO'ing and doing it all over again. Is this an extreme case? Yes, but my point being is if you want something bad enough you will make it happen. Even on my off days from my night job there are few things I would like more than to come home kick off my shoes and relax with a cold beer and a nice cigar but I don't make exercise optional and do it anyway as soon as I walk in the door just to get it over with. Because I know that in the same time I could spend dicking around on youtube and smoking a cigar I would have gotten an ass kicking work out in and been done for the night.
With that said, if you can only do one or the other Diet vs Exercise I say change your diet. I should specify there is no "Diet" that will work for you it is a lifestyle regardless of how cliche that may be. You cannot selectively change you diet and expect things to just happen, its all or nothing, you just need to start eating healthy end of story. I am not saying you can never have another soda or cheeseburger what I am saying that you have to earn them and honestly if you commit the time and effort in the gym you will not want to reverse all that hard work for a few minutes of mouth pleasure. I think the occasional cheat meal it totally healthy both physically and mentally and for me personally those cheat meals drive me to work that much harder the rest of the week. But I think you will find once you start eating healthy you will not be craving as much if any of the junk you were consuming before just because of how good you will feel eating real food.
As far as exercise is concerned if you have bad knees but do ok on a bike, do it, do what ever it is that you want and will continue to do. If you hate a workout you are probably not going give your all and you most certainly wont stick with it. I used to think yoga was the stupidest shit on the planet and as someone who also suffers from two bad knees I absolutely love it now. It is basically zero impact, static exercise combined with stretching. Honestly if I could only do one exercise the rest of my life it would be yoga and that is coming from a beer drinking, cigar smoking, ex race car mechanic. Thankfully I am still able to do higher impact stuff but you are going to have to humble yourself to do this so don't be afraid to step out of your comfort zone and try something new you just might be surprised.
This is going to sound silly but the tipping point for me was my chick making me watch a documentary on netflix called fat, sick and nearly dead. If you need any motivation at all, watch that movie. The truck driver in that movie (I think his name is phil staples) is the most inspirational mofo on the fkn planet to me. Once I saw the transformation he went through I decided enough was enough and if he could do it I have zero excuses. And literally from that day forward everything changed I wish I could tell that guy how much he has impacted my life because he literally inspired me to do a 180. We did the juice thing for a while about 3 months to be exact before switching to an all around healthy diet of lean meat, and lots of veggies. But in those 3 months of drinking juice twice a day everyday we lost over 70 pounds between the two of us without even starting exercising. Once that happened it was game on an we haven't stopped since.
Honestly anyone can do it, you just gotta put in the work, if you really care about yourself and your future you will make some changes and stick with them this cannot be a temporary thing. Lastly if you need some extra motivation or have any questions at all or just wanna talk about this pm me, call me whatever and we can talk about this.
As far as diet is concerned googling lean recipes is a good place to start, print out anything that sounds good and make a binder full of recipes and just toss the ones you dont like.
We cook from here quite a bit
Dolce Diet and everything its pretty tasty and obviously not bad for you.
As far as exercise is concerned we started with P90x did it non stop for over a year and a half before giving insanity a try, I thought insanity was too high impact and brought on knee discomfort for me so I went back to p90x for another few rounds. Now I have moved on to kettle bells which I currently love and have been doing keith webers extreme cardio kettle bell workouts a few times a week and get my ass kicked and they are also pretty low impact but do incorporate a lot of squats.
Also if you are going to juice, my advise is just put in EVERYTHING don't juice for taste you can chug that ish anyway. We would literally go to the farmers market every saturday spend 60 bucks and get enough produce for the both of us to juice twice a day everyday that entire week and we would literally make a pitcher of juice containing.... Kale, Carrots, brocoli, ginger, tomatoes, oranges, apples, beets, celery, spinnach, cilantro, parsley, berries, bok choi whatever looked good. One secret I will say is ADD LEMON. Lemon is an important one because at least for me it cuts the green taste down dramatically.
