If your computer has Microsoft Office installed, you have the "Office Picture Manager" program, which is excellent for simple tasks like resizing & basic colour tuning. On Linux, it's got to be The Gimp, which you can also get for Windows & Mac at no cost.
I agree with the others: always keep the originals. When working with digital media of any kind, incl. sound and video, it's easy to do things that cause information & quality to be lost, and once it's gone, it's gone. You can always archive originals to DVD+ROM or whatever, but burn multiple discs, don't trust everything to a single burned disc.