You must go to:
Windows 7/Vista: C:\Program Files (x86)\Pst\E-Prime 2.0\Program\LicenseManager.exe.
Windows XP: C:\Program Files\Pst\E-Prime 2.0\Program\LicenseManager.exe.
Double click on that file and it will bring up the dialog you are looking for. Enter your new information and start E-Studio.