If you are a system administrator, you can modify a user account by doing the following:
1. Click on your name on the top right-hand side
2. Select "Account Preferences and Profile Overview"
3. Select the "Actions" drop-down menu
4. Select "Modify"
5. Select the necessary additional user roles and select "Save"
Please note, the user may need to log out and log back in for the account to take effect of the new user role.