After you create a virtual machine, you can clone it to a template. Templates are master copies of virtual machines that let you create ready-for-use virtual machines. You can make changes to the template, such as installing additional software in the guest operating system, while preserving the original virtual machine.
You cannot modify templates after you create them. To alter an existing template, you must convert it to a virtual machine, make the required changes, and convert the virtual machine back to a template. To preserve the original state of a template, clone the template to a template.
If a load generator is running in the virtual machine, stop it before you perform the clone operation.
Verify that you have the following privileges:
on the source virtual machine.
on virtual machine folder where the template is created.
on the destination host, cluster, or resource pool.
on all datastores where the template is created.