Apparantely,
Я хочу быть повыше - I want to be taller.
Я хочу чего-нибудь послаще - I want something that tastes sweeter.
Может ударить тебя побольнее? - Maybe I need to hit you more painfully?
Будь повежливее! - Be more polite!
But there's a little "but" here, and this "but" is that this "по-" thing sometimes could be translated as slightly, like slightly taller, sweeter and so on. But this is a very sutle thing though.