To deactivate a login please go to 'Review/Edit/Add Logins'.
Click on the Login Name you would like to deactivate.
Scroll all the way down and deselect Active and you must enter a password. The password can be anything you would like and click OK.
To update a login's privileges, click on Edit.
Here you can select and unselect their access types.
Click OK once the selections have been made.