If you have not already read the Roles and Permissions Overview, I recommend you do that first.
If you want to change the access level someone has (known as their "Role") this is how to do that:
You must have either an Administrator, Board Secretary or Chair role yourself
Click on the People and People List
Click on the context menu at the end of the row -Edit
When the pop up box opens you can:
Tick or un-tick the Board Member box (if this box is ticked the person will be listed as a Board Member on the Agenda/Minutes, be able to vote, and also allow them to view any confidential folders in Governance Documents).
Tick the box next to their new role
Click on Save Changes.
Notes:
If the person is online at the time, they may need to log out, and then log back in for the change to take effect.
A person cannot have the role of an Executive/Guest and have the Board Member box ticked.