After logging in with admin and admin as username and password in your new tikiwiki site,
- change the password of 'admin' user
- In the left side menu click on :: to the left hand side of Admin and click on Users
- Fill the 'Add a new user' form (you can ignore 'Batch upload...') and press Add.
- The new user you created will appear in the list of Users below. Click on the key icon having the tool tip of: Assign Group (Active) for this new user.
- In the table at the bottom, click 'assign' for the last record having the name as 'Admins'.
- Log out as admin and log in using your new user account that has been given admin privileges.
Flash screen recording: I created a small flash movie about adding a new user and making him admin. For what it is worth, it can be viewed at http://sridharkatakam.com/sri-addons/flashots/tikiwiki/CreatingANewAdmin
(Has no sound)