Grace,
Corporate statutes do defer to the governing documents on how Officers are elected/appointed.
Had your documents been silent, then the Board would have appointed them.
Per corporate statutes, specifically
617.0842, the board may appoint someone to the office once a resignation is submitted.
My suggestion:
Each person who wants to change positions submits a letter of resignation in writing.
The Board, at the next meeting or via action without meeting (ideally at the next meeting), appoints those individuals into different officer positions (or anyone else the board believes should fill the positions).