Certainly you can. You need a graphics program. It can be as simple as Windows Paint, but for a better job you'll need a better program. Paint Shop Pro, Adobe, MacroMedia Fireworks and many others are quality programs. A forum search for graphics programs should yield results. Word of warning, the learning curve is steep, people make a living as graphics artists. I've played around quite a bit and wouldn't call myself anything but a hack in this regard.