Confirmation Email Short codes

I am using a membership plug-in called WP-Members and it is furnishing me all of my required fields. Of course it provides for: user name, first name, last name, etc. This is perfect. Now when a person signs up for a yoga class, the Appointment+ plug-in has the following fields:

SITE_NAME, CLIENT, SERVICE, SERVICE_PROVIDER, DATE_TIME, PRICE, DEPOSIT, BALANCE, PHONE, NOTE, ADDRESS, CITY, EMAIL (Client's email)

How can I have the field for: FIRST_NAME & LAST_NAME included. User names are too difficult to know who the client actually is.