Take it once before you register again. You might not need to take it again, and that'd be a waste. You should move it earlier if you feel prepared though so that your app can be processed faster. Make sure you make the deadlines for the schools you're applying to though. Like the school I'm apply to lets you take the GREs no later than november 14th, otherwise you won't be considered.
You get your V/Q scores immediately after, so you can register again after that if you feel like you need to. Hope this helps!