The operating system version is specified when you create the virtual machine. If you’ve specified the wrong operating system version or you plan to upgrade the already installed guest operating system, you will need to change the guest operating system version.
Here are the steps:
1. Power off the virtual machine.
2. Select the virtual machine from the library and select Player > Manage > Virtual Machine Settings:
3. Go to the Options tab and select General. On the right side of you screen you should see the Guest operating system and Version menus. Select the new operating system and version and click OK: