If a customer has an active pass, it is possible to renew it for another term before it expires.
Pull up the customer in Global Sales, select the desired pass and add it to the shopping cart:
Since the customer is an active pass holder, you will receive this message.
Clicking "Yes" at the message above will bring up a new window where you can confirm the parameters of the future pass:
Verify that the term of the future pass you are selling is correct. The Member Begin Date should start the day after the current pass expires. Clicking "Continue" will add the pass to the shopping cart and the customer will be charged the rate of the pass.