Giving users administrator privileges on the control panel is very straightforward once you know where to look: Hosting Order Access, one of the dropdown options from the ​control panel page for a user that already has this access (such as the first user given to you for a new account).

There it describes itself:

Hosting Order Access allows you to give other users the ability to create new users, email accounts, and other settings related to your account. Before giving someone access to your account, you must either create a user account for them, or they will need to tell you what their user account login is. Next, create a new item here, entering their login name where it says "Login".