To Re-Install OS, go to VPS Management Page and click on "OS Re-Install". First select the Distro of the operating system you want to install. Then select the architecture of the operating system which is to be installed. Then enter the password which will be set as the password for the Root User to log-in and then press "Reinstall". Then wait for a while till the OS gets installed.
Note :- Please Make sure you had performed data backup of the VPS. Reinstall os Will create Fresh VPS without any data .