First, (once you login into the firstname.lastname@example.org account) create the new one using User management:
Click the Add button:
In the window that opens, fill in all the required fields, using your new data (your personal Email and the rest).
Check the box in the Administrator check-box:
After all these actions go to the admin panel already with your new account (new login and password), and in User management, delete the demo account:
(make sure that there is an administrator on the red background next to your new account).