The majority of User details including access levels is updated via Data Feeds from your organisation.
In some cases, you, or your organisation may have high enough access level to update a users level, but note that if user settings are controlled by a Data Feed, the next sync will generally overwrite the changes you make.
It is advisable to make sure that you check how your Users and Access levels are controlled by contacting your relevant Food Safety Manager, Consultant, Help Desk or Head Office.