Group Theme Restrictions
Click on the "Users and Groups drop down and select "Manage Groups".
Here you will see a list of all current groups. Find the group you want to edit and click the "Actions" drop down and select "Change Group Theme Restrictions".
Select the theme from the ordered list then click "Move Group Members to Theme".
Individual Theme Restrictions
Click on the "Users and Groups drop down and select "Manage Users".
Related articles