Before you change the hardware compatibility of a virtual machine, you should be aware of certain considerations and limitations.
For Workstation 5.x, 6, 6.5, 7.x, and later virtual machines, you can change the version of the original virtual machine or create a full clone so that the original virtual machine remains unaltered.
If you upgrade a Workstation 5.x virtual machine that is compatible with ESX Server to Workstation 6, 6.5, 7.x, or later, you cannot use the Change Hardware Compatibility wizard to later downgrade the virtual machine to an ESX-compatible virtual machine.
When you upgrade a Windows XP, Windows Server 2003, Windows Vista, Windows 7, or Windows 8 virtual machine, the Microsoft product activation feature might require you to reactivate the guest operating system.
Using Workstation 9 or earlier, you cannot change the hardware compatibility of a shared or remote virtual machine.
Using Workstation 10 and later, you can change the hardware compatibility of a shared or remote virtual machine. However, you cannot down grade a previously created virtual machine.