With appropriate permissions, you can manage the users assigned to a role from the Roles List.
Use the fields at the top of the Assign Users to (name) role page to search for a user. You can select and clear check boxes to add to or change the users assigned to this role; clearing all check boxes removes the role from all user accounts.
To manage a role's users
In the main menu, click Setup and then click Roles. The Roles List opens.
Locate the role and, on that row, click Users. The Assign Users to (name) role page opens.
Select and/or clear checkboxes to assign users to or remove them from this role.
Click Save.