I use
Gimp for all picture-editing purposes. It's completely free, and has a huge amount of thingies, some more useful than others. OK, it is a bit bloated, but if you happen to have some extra space, I suggest you download it. It's not Photoshop, but the price is right.
If you don't feel like swimming your way through the official site for a windows wersion, just
download the installer.
And you'll also need the
GTK+ 2 runtime environment.