Only the existing Super User can designate someone else as a Super User.
If you are the current Super User, you may hand over this status by doing the following:
Go to Business Settings
Click on Staff Roles
Click where it says Super User next to your name
Select a new Super User from the drop down menu
Hit Save
Any roles can be changed in the Staff Roles section by clicking on the orange arrow in the Staff Group column and selecting a new role from the drop down menu. Always be sure to hit Save!