[lessd]

1. call tivo and have them make the switch
or
2. Use your tivo.com account (create one if you don't have one).
got to tivo.com
click on manage my account
sign in
click on change service number
if you have more than one tivo you'll have to choose which one to change
enter the service number of the new tivo
click on change

Warning! This will transfer service from TiVo Service Number [old Tivo] to the new TiVo Service Number. [Old Tivo] will be deactivated.

You may not get any rebates if you do things this way!!