Designing your web site
You will want to crop and resize your images so they're the right size for your site
Fireworks is an excellent image editing software package. It's specifically designed for web graphics.
The following three links will take you to a very good tutorial that will explain the basics of Fireworks.
Cropping Cut out the area of an image that you want.
Resizing Shrink the file so it won't take forever to load.
Exporting Save the image in a web-friendly format.
Freeware Image Editing
PhotoPlus is top rated by PC Magazine
These are three freeware image editing software packages that are free for the download.
On-line Image Editing
Yes, you can edit images through a web site.
See a review of 20 online image editors
http://www.splashup.com/ is a good one.
What's the difference between jpg and gif?