Handling your Keyring
The GNOME Passwords and Keys allows you to browse, edit and delete items in your Keyring.
This is also the best way to control the keyring username and password. See GNOME Passwords and Keys for more information.
A workaround is to use the Find Files/Folders utility to locate the Keyring folder on the machine. When located, proceed to delete all the files inside this folder. The next time the application is run and references the keyring, a prompt will issued requesting a new username and password. The newer versions allow a blank username and password, but discourage such practice for risk of breeching security.