Any current "Captain," can upgrade any other group member to the role of "Captain" at any time (or downgrade an existing one...) Here's how:
Go to your Admin --> Members page.
Find the person to whom you want to grant admin privileges, and click the small blue "up" arrow to the far right of their name.
When prompted, confirm their upgrade to the role of "Captain."
You can downgrade by the same process.
Note: On every PRO Account there can be multiple "Captains," but only one "Captain-Admin." Captains have all the rights of the Captain-Admin, but with one difference: the Captain-Admin is the one with access the account's billing and credit card information. If you would like to transfer the role of Captain-Admin to another person, please contact us at firstname.lastname@example.org.