Beside each privacy group are 2 icons (a green plus icon and a red minus icon)
The green plus icon allows you to add members to the privacy group.
Click the green plus button and in the keyword field type the username or part of the username you wish to add.
Click the checkbox beside the user(s) and click Add.
A number will be displayed beside the name of your privacy group which indicates how many members you currently have in this privacy group.
To remove a member from a privacy group, click the red minus button beside the add button
Place a checkmark beside all the members you want to remove and then click Delete.