To edit a Recurring Membership's payment plan, head to Memberships >> select the desired membership >> click 'Edit' next to the plan you would like to change:

Here you can:

It is not possible to edit the billing day of the month or first payment settings, or minimum commitment length on an existing plan, so if you wish to do so, then please add a new payment plan instead with the settings you wish to sell going forward and close the existing payment plan to new purchases.

See this video for steps on how to mark an existing plan as not for sale and create a new plan.

💡You will still be able to see the old payment plan after you've set it to "no, this payment plan cannot be selected", but customers won't see this from their side. Existing customers will remain on this plan, but new customers won't be able to purchase it.