Photoshop is arguably the most powerful image editing software around. It also cost an arm and a leg. In fact at around £600, it probably costs more than the computer you’re installing it on.
However, there is an online version that you can use free of charge. Obviously it doesn’t contain all the features of the full program but this cut down version is still pretty powerful.
Find it at http://www.photoshop.com/tools
You’ll also find a range of smart phone apps for image editing on the move