Your Will should utilise your current full legal name. In the alternate name section, you should only include previous names that you still hold assets in. If you hold assets in multiple previous names, you can add them into the Alternate last name box as follows.
For example, in the boxes you can fill it out like this:
Alternate First Name: Sally
Alternate Middle Name: Jessica
Alternate Last Name: Parker, Sally Jessica Smith, Sally Anne Smith-Parker