to downgrade the virtual hardware just download and edit the vmx file from the VM datastore folder and change the value from 13 to 10 or 11, save the file to your desktop and upload back into the VM datastore folder, see links below.
How to Downgrade VMware ESXi 5.5 Virtual Machine Hardware Version to 9 from 10
Editing configuration files in VMware ESXi and ESX (1017022) | VMware KB
Note: make a backup copy of the original .vmx file just in case of any problems!
Steve