First go to Vcclhosting.com and Login to your Client Panel and open the menu shown in the image below.
Now from products & services menu go to the hostname or the server whose operating system you want to re-install
Now confirm the currently installed OS and it will be fully Re-installed all the data will be wiped, Make sure to backup essential data.
Now once you select the OS Varriant you will be prompted.
Confirm the pop-up to begin Re-installation.
The New OS will take approx 10-15 minutes to be reinstalled.