Press "Settings" and then "Users" in the board you want to change the authorization of a user in. Click the symbol with three dots and select "Edit" on the user you want to change.
Under "Authorization" there are three different levels: Administrator, Observer and Restricted. When the changes are made, click "Save".
Description of authorization:
Administrator: has access to all materials in the organization. This level is required to be able to upload documents, create new meetings and so on. This is the recommended level for board members.
Observer: has access to view and read all materials available for the organization, but can not, for example, upload documents or create new meetings.
Restricted: can only see the material that has been actively shared with them or assigned to them. For example, a user can only see his or her own to-do tasks and the meetings to which he or she has been invited to.