Issue: You need to install windows updates or make other changes to a Windows based VMWare Template.
Solution: The following steps will convert the template back to a VM, allow you to apply any updates or changes and then sysprep the VMWare template and finally convert it back into a template.
1) Right click template, click convert to Virtual Machine
2) Power On the Template, and logon to it (open console)
3) Apply windows updates or other changes, reboot
4) Logon to template again and run the following from command prompt:
C:\windows\system32\sysprep\sysprep.exe /generalize
Select “Shutdown” option.
Select the “Generalize” checkbox.
Select the “Generalize” checkbox.
5) Right click template in vCenter and select ‘convert to template’, this will convert the VM back into a template.