See here for more useful information
User names and passwords
Changing your password
It couldn’t be simpler to change your password.
Click on Change password and log in using your regular University details. You should be presented with the ‘Change Password’ page. In the relevant boxes, just type in your old password and then whatever you wish your new password to be.
Change to your answers
Once you've set your answers you can change them and your third question at any time. Just log in and click on ‘Password Challenge Response’. Make sure you un-tick the ‘Use Stored Response?’ box.