[Gavin B.]

It's a pretty opened ended question, but like others have described, once you work out what you want to change, then you search for a similar "hack" on this site - and it contains instructions on which files you much open up in a text editor and modify to make the hack work with your particular board.

It's like saying "how to I modify my car", you can do whatever you like to it really, YOU just have to decide what your goals are exactly.

If you have problems, you can always ask on a site like this and people are more than willing to install hacks for you in exchange for money (or some other service like hosting or whatever).