1.You shouldn't really ask for advice in ongoing games.
2.You may not have a significant advantage anyway: the entire point of some openings is to give up the centre, and undermine it later. Having a good centre doesn't gift a win.
3.Try to fully develop pieces and build an attack. Try to keep your opponent passively defending, but remember he will likely attack your centre.
On a related note, apologies if this is slightly off topic Conflag, but I invariably find myself a minor piece down at the end of the opening. I can't put my finger on what is going wrong particularly but wondered if anyone can also advise on a good solid opening that may help me erradicate this.
It's not that simple.
Maybe you can create outposts for your pieces in the centre, or prevent your opponent from playing in the centre. Space advantage.
Keep playing. You might want to study some middlegame lessons/books/etc. for ideas. There's no magic formula or one way to proceed. Pawns on e4 and d4 is not evidence of a big positional advantage that can be "converted" into a win.
You asked a perfectly legal generic question about how to handle a type of position rather than a not-allowed question about a specific position in an ongoing game. But the thing is, you could get better, more useful help asking about a specific position, and the better thing to do here is wait for your game to be finished, and then ask about that specific game and the pawn center you had and whether you used it well or not. It can be a good idea to make notes on those questions because as the game heats up one tends to forget all about the early questions one had as new seemingly more pressing questions arise later in the game.
I'd like to know how to convert having control of the center into a material advantage or win.If I have pawns on e4 and d4 what do I do?