You can assign the Owner role to people when inviting them to your team.
You may also change their roles later by following these instructions:
Click on the Edit icon (the pen icon) beside the person’s name, and proceed to edit.
In the Edit User window, click on the 'Role' dropdown menu to expand the options. When you select a role, its description will be shown in a yellow box below.
Select the 'Owner' role for the user you want.