To change user permission, go to the Users/User Manager and find the user you want to edit and click on Edit link.
You can change user level and permission there.
Users can not change their own level and language permission (even super admin).
User Levels
There are seven types of user level:
User (0)
Normal user. Doesn't have access to the back-end.
Author (1)
Author can login to the back-end and can send an article. Posted article will go to the waiting list. Publisher can approve the article and publish it.
Editor (2)
Editor can login to the back-end and publish an article without higher level approval.
Editor also have permission to add tags and assign picture to it from Tags.
Publisher (3)
Publisher can login to the back-end and publish an article without higher level approval. Publisher can also manage files from File manager and Approve the article that author level posted from Posts/Post Manager/Wait.
Publisher also have permission to add tags and assign picture to it from Tags.
Publisher can not see or manage posts with page type.
Manager (8)
Manager has full access to the posts, Categories, Tags, Menus, Translate and Widgets.
Manager can also manage extensions and install or update them.
Administrator (9)
Administrator has all permissions that manager has.
Administrator can also manage users (Administrator level and lower level users) and change Settings/Head and Settings/Security settings.
Super Admin (10)
Super admin has permissions to everything. Only super admin can create another super admin.
Language Permission
There are three types of language permissions:
Permission to all languages
User has permission to all languages. Some back-end settings need permission to all languages to view. Level zero users can have access to all languages in the front-end.
Permission to nothing
User has no permission to any language. Level zero users can not even login in the front-end.
Permission to one or more languages
User has permission to specific language(s). Level zero users can only login in the specific language(s) in the front-end.
To change the permission for back-end widgets by user level, go to the Extension settings.