There are no easy solutions here. Understand that what you're feeling, the act of hating yourself, is extremely unhealthy and probably won't just go away on its own. Severely low self image or self worth issues probably stem from a number of bad experiences and you can't just flip a switch to fix that.
I'd seriously look into therapy to atleast talk some of these issues out.
If you're trying to do this on your own, look for books and legit online resources on the subject.
Hit the gym or start working out from home. It takes time, but little by little, you start feeling a bit more confident.
Find new hobbies or things to learn. The better you become at something, the more you'll value yourself.Cook, Draw, play a video game, pick up an instrument, write, whatever.
And finally, try not to compare yourself to others. We all have different goals and we hit them at different times. Some of us bloom much later than others.
But again, none of this comes easy. If you really want to change the way you think, you gotta put some good work into it