Not from Jammed. Membership payments go through your own Stripe account, so refund them from your Stripe dashboard.
Worth knowing: removing a membership cancels the subscription immediately and stops any further payments, but it doesn't return anything for the part of the period already paid for. If someone paid on the 1st and you remove them on the 3rd, nothing comes back automatically.
Moving someone between two paid tiers is different. There the difference for the current period is worked out automatically and adjusted on their next invoice, and the member is emailed to say so.
Membership fees and booking refunds are completely separate. Cancelling a booking never affects a membership payment, and vice versa. See [[Cancellations and Refunds]] for how booking refunds work for members.