If a customer has expressed interest in moving from one membership to another, you can make this happen by heading to their profile (click Customers > Customer List > search for them).

From their profile > click the dropdown menu to the right > click Transfer > select the timing option that fits with the circumstance.

If you're wondering what the red text on incompatibility at the bottom of this message means, this auto-setting ensures the customer's existing bookings match their new memberships benefits.

In other words, if the original membership was applicable to certain classes that the new membership is not applicable to, the customer will be cancelled out of those classes after the transfer is complete.