To edit an existing access level, navigate to the Viewing Access Levels tab of the User Manager (Users → User Manager → Viewing Access Levels). Then
To create a new access level,
Access levels control which users can view which objects on your site. Objects include menu items, modules, categories, and component items (articles, contacts, and so on). Each object in the site is assigned to one access level. User groups are also assigned to each access level.
If a user is a member of a group that in turn has permission for an access level, then that user can view all objects assigned to that access level. It is important to understand that user groups can be arranged in a parent-child hierarchy. If so, then a child group has access to all access levels that the parent group has access to. So you don't need to assign a child group access to levels that its parent group already has access to.
At the top right you will see the toolbar: