Changing back to the Free plan is easy but you will need to cancel the monthly subscription manually. You can launch the payment portal from the plans manager by selecting the Payment Portal button under the subscribed plan.
This will launch the payment portal and allow you to select the subscription and cancel it. This will stop all future billings. If you do nothing else, RMMmax will demote your team to the free plan after the grace period ends. The grace period ends 15 days after your billing cycle has expired.
Then if you want to move to the Free plan immediately, you can select the subscription button under the Free plan. Afterwards, log out and back in for your browser to fully update to the new plan.
