Information requested when changing the Eloqua instance name

The information required when changing the Eloqua instance name is as follows:

Current Site ID:
Current Client Code/Login Prefix:
New Site Name:
New Display Name:
New Company URL:

I would like to know what each item means or where I can find this information.

(I am also wondering if it is acceptable to submit only one of the two items, either the Client Code or the Login Prefix.)

Thank you.