If you have a Windows XP (Home or Professional edition) virtual machine, you can upgrade to one of the supported Windows Vista. During such an upgrade-in-place only the operating system itself will be affected, and you don't have to reinstall all the applications in the virtual machine.
To upgrade to Windows Vista correctly you should do the following:
Launch Parallels Desktop for Mac.
Open your virtual machine and log in to the Windows XP operating system.
Choose Actions menu > Prepare Windows Vista Upgrade from Parallels Desktop menu.
Insert the Windows Vista upgrade CD and follow the wizard's instructions.
- When you're finished with the necessary preparations, the virtual machine automatically starts.
Upgrading to Windows Vista starts. Follow the on-screen instructions.