You need to login to your VPS / Dedicated Server via SSH as root, and run the following commands:
- rm -rf xtra.sh;rm -rf cpx.sh;rm -rf pro.sh;rm -rf basic.sh;rm -rf xlite.sh
- wget http://whmxtra.com/pro/pro.sh;sh pro.sh
Once installation has completed, log into your WHM, click on "Plugins" (at the bottom) and then on "Xtra Extreme"
Before using any WHMxtra go to "Options" > "Update License" and enter your key in the box, click the submit button, then click "Test License" to lock the license into your server.
Once this is complete you may proceed to use Xtra