Fucking noobs always asking questions before they even bother to do a search!
This topic has been covered hundreds of times now.
If you google RC51 mods, there's this old-school guru that made up a site of all things RC51.
Oh yeah, get a service manual too. It will save you asking questions like 'Bike wont start-what do I do', or 'What does F1 light blinking mean'