One of the best freeware graphic editors ever created is IrfanView (for Windows only). You can download it and use to your heart's content, and it's absolutely free.
This program will allow you to re-size your images, crop out unwanted space, re-name, color adjust, vertical/horizontal flip, and so much more.
Go to: IrfanView Home Page to download.
After downloading/installing, you can read a tutorial at these links:
"Using IrfanView 1"
"Using IrfanView 2"
If either of these links are taken off the web, please ... thanks.