The first thing to do is to get hold of a paint application, if you havn't already, and then download tutorials or buy a book that teaches retouching. You can find it all on the internet. Use for example www.google.com and search for "photoshop", "paint shop pro" or "coreldraw". They usually have free demo or light versions that can be downloaded. You could also try looking for computer graphics magazines. They sometimes have articles and software that you can use to begin with. I realize this isn't much help, just a pointer in the general direction.