Please check these top knowledge base articles which may cover the question you have:
Windows 8 Update - Critical and Urgent Windows 8 Service Advisory
Windows 8 upgrade: step by step instructions and tips for Parallels Desktop users
How can I upgrade to Windows 8 and keep my current Windows 7, Windows Vista, or Windows XP virtual machine?
Which Windows Virtual machines can be upgraded to Windows 8?
How to migrate Windows 8 PC to Parallels Desktop 8 Virtual Machine?
Can I buy a copy of Microsoft Windows 8 from Parallels?
Parallels Tools features stopped working after Windows 8 upgrade: \psf\Home\Desktop error
Windows 8 VM does not start: how to repair Windows 8 installation?
Can I boot Windows 8 VM straight to Desktop?