1) Go to your Home Folder
2) In the address bar type ~/.gnome2/ (if you don't see the address bar, click the little icon with the paper and pencil that has a tooltip like "Toggle between ...")
3) Delete the folder called keyrings
Next time you run a program that wants to use the keyring you will be asked to type a password. This password doesn't have to be the same as your regular password.
If you are comfortable with a terminal, the command is:
rm -r ~/.gnome2/keyrings