Most of the users want to change the template name, so here is the procedure for the same:
Step 1: Login FTP or Cpanel
Step 2: Go to whmcsDir/templates/
You will see all the templates folder here.
Step 3: Change the desired template name by renaming the folder of the template.
Now follow these steps to assign the renamed template.
Step 1: Login WHMCS admin
Step 2: Go to Setup > General Settings > Template
Step 3: Now assign the template that you have renamed.