We get asked all the time what is the best photo editing software and of course it easy to say PhotoShop by Adobe, but this is not practicle for your average Joe, as it is not easy to use, it is not cheap to buy and needs training to get the most of it. It also needs to be installed on a specific pc.
The best option I can recommend to people who want to do the basics to images such as reducing the size of the file, in terms of megabyte size and in width and height and maybe saving a large image to an image thay can use to insert into their website would be an online software as a service called pixlr.com. This is ideal for our clients who are on the move and want to edit images from their 12 mega pixel cameras that are too large to insert in the website via the content management system
This online tool has a number of options, you can use it in Pixlr Express mode to do the very basics or you can enter into the more complex tool to really do the same kind of things you would like to do in Photoshop.