Tutorials: How to reset your Joomla 1.5 password
OK this is a bit tricky as Joomla 1.5 uses its own encryption algorithm. You will have to login to Cpanel, click PhpMyAdmin, select the database and click on jos_users (or prefix_users if you've used another db prefix). Click on the edit icon and put this in the password field :
Click OK. Your password is now cmsdemo . Please change that to something else immediately as it's not safe.
Another way to update the password is to run this query from PhpMyAdmin:
UPDATE jos_users SET password='50e158580f8cd900d1c319c4c08a8a74:oDzHxt8lPSpvbKYf2vW6Vxp9zsw5SlIZ' WHERE usertype = 'Super Administrator';