It's simple... If you want to top it, get a pair of scissors, follow the main stem all the way to the top, choose a spot down a couple leaf nodes down from the top, and cut it off, just snip the main stem right off. Pretty much impossible to do it wrong. Just don't go too far down. 2 or 3 leaf nodes down will be good, it will bush right up for you.

Can you tell its sex yet?