The password is stored in the database and it's md5 "encrypted". If you have access to phpMyAdmin, find your entry in the gl_users table and change the value for the field passwd to 5f4dcc3b5aa765d61d8327deb882cf99 (copy and paste that into the passwd field). After that you should be able to log in with the password "password" again.
But if you've been hacked (how? which Geeklog version are you on?) you should really check your site for other changes, e.g. files that shouldn't be there.
