Complex sentence: If an arrangement is unsatisfactory, members may leave their group and join another one; they are required to submit written notice 30 days before leaving, or they will be charged the following month's fee.
Split into simpler sentences: If an arrangement is not working for any reason, members may leave their group to join another one. To do this, members are required to submit written notice 30 days before leaving or they will be charged with the following month's fee.