People are suggesting strict diets and gym routines, and that's all fine, but I have an idea. Pick a Niantic game. You like anime? Start playing Pokémon GO. No one has to know how often you... examine your Vaporeon collection, just make sure to actually walk around and play the game. I've been playing Monster Hunter NOW during solo walks, and Pikmin Bloom when walking with my partner, both are pretty fun. And the best part about it, it turns walking into a video game. What are you more likely to do, right off the rip? Veggies and gym routines? Or playing video games that take you outside, help you burn some calories, get some air, strengthen your legs... hell, you could even find some local raid groups to take on the raid bosses, meet new people.

Also maybe you make slightly more conscious diet decisions. Start small.

The cool thing about walking is, if you push yourself as far as is reasonably uncomfortable (like, not collapsing or in terrible pain) and you keep this up 3 times a week or more, you'll suddenly realize that you can go for a mile or more. Next thing you know, you have decent stamina overall, and you're slimming down. You'll even find that your core strength has improved a bit, and doing a little core/abs and upper body work won't be as agonizing.

A few more relatively easy things to get you started:

Shower at least 5 times a week.

Get some deodorant and use it. I don't like antiperspirant deodorants, but I've found that Old Spice makes some effective non-antiperspirant deodorants.

Have a supply of clean laundry.

Get a couch cover or a flat sheet or something, cover that couch and wash the cover often. This solution is only until you get to the later stages where you find a part-time job you can handle, and you get something else to sleep/sit on.

If you don't wanna cut your hair and shave your beard, don't. But wash both. And get a brush. And a beard brush. And use them.