ResolutionUpgrade from Parallels Server 4 Bare Metal to Parallels Server 5 Bare Metal can be performed by following these steps:
1. Burn Parallels Server 5 Bare Metal ISO to a DVD disk
2. Insert the disk to optical drive of the server
3. Boot from the DVD
4. Follow the wizard and select the Upgrade an existing installation option, and click Next. If you have more than one installation of Parallels Server Bare Metal on your physical server, choose the necessary installation on the drop-down menu.
Upgrade via command-line tool vzup2date is not supported yet.
For more information refer to Parallels Server Bare Metal Installation Guide