How do I make somebody an administrator?

If you're an administrator yourself, you can add and remove administrator rights in the popup dialog of each user. Click on the user's name to open the popup dialog, and then click "Add administrator rights" in the bottom of the dialog to make him administrator:

And click "Remove administrator rights" to remove the rights from somebody who is administrator.

There must always be at least one administrator, and Scrumwise will ensure that this is always the case, no matter what.