www.robertsrules.com
this is link to RRO. copy and paste it into your browser. here is a FAQ regarding just your situation
Question 20:
How can we get rid of officers we don't like before their term is up?
Answer:
It depends. If the bylaws just state a fixed term for the officer, such as "two years," or if they say the officer serves for a specified term "and until [the officer's] successor is elected" (or words to that effect), then the group must use formal disciplinary proceedings, which involve the appointment of an investigating committee, preferral of charges by such a committee, and the conduct of a formal trial. The procedure is complex, and should be undertaken only after a careful review of Chapter XX of RONR.
On the other hand, if the bylaws state a term for the office but add "or until [the officer's] successor is elected," or contain other wording explicitly indicating that the officer may be removed before the term expires, then the election can be rescinded (see Chapter 7 of RONR In Brief) and a successor then elected for the remainder of the term.
Of course, if the bylaws themselves establish a procedure for removal from office, that procedure must be followed. [RONR (10th ed.), p. 642-43.]