If you don't have a copy of Photoshop, fear not, you can likely do everything you need to do with/to an image using a free online photo/image editing application. I have been watching online image editing programs develop for awhile now. I have utilized them a number of times for classes and person use. I am truly amazed at their capabilities.By the way, these programs are particularly sweet if you are using a netbook with limited memory and processing power.
Some of them such as Aviairy have a number of tutorials available. Give them a try, you will be amazed at how well the work!