just lose some weight, eat healthy and exercise
you're not going to dramatically perk your boobs up or change their shape, they may look a bit less droopy if there's less weight on them though... they may not and in that case don't worry, you can get bras/bikinis which push them up and make them look good and tbh as far as anyone seeing you naked, boobs are boobs, they'd have to be pretty horrendously deformed before they became disappointing