As an admin, you can set user permissions either when inviting a new user or by editing an existing user.
To do this for an existing user, click on "Users" in the left-hand navigation and then click the pencil icon. The following screen will appear:
The bottom drop down is where permissions can be found: Admin (with billing), Admin, Manager, Author, Contributor and General. Click the applicable permissions and then click "Save Changes."
*You can learn more about permission levels here.