In order to edit a security role for a user you need, when logged in as an administrator, to click the User Accounts button in the menu.
Click the user you want to edit the Security Role.
Click Manage Roles for this User at the bottom.
By checking “Send Notification” the user will be sent a notification email to inform him of the role modification.

From this page the administrator can:
- Add a role for the user
- Cancel the role for the user