Welcome to the Community,
the easiest way to rename a VM's files is to Storage vMotion it after it has been renamed in the inventory.
If you are going to rename the files manually you need to be very careful (especially if a VM has active snapshots). Renaming the files will also require editing the configuration files, i.e. replace file name references. Virtual disk files have to be renamed using the vmkfstools command line utility. Renaming the files manually also requires that you remove a VM from the inventory and add it again after the modification. This can cause additional administration overhead in case you are using third party tools (e.g. a VM based backup application) which rely on the VM's VMID.
André