Click on the Reinstall button. You will see a list of all available operating systems. Note that if you have a KVM, you're only going to see KVM templates. If you need to switch virtualization technology, you need to order a new VPS.
Select the button to the OS you want to install and then click the reinstall button.
You will receive a confirmation of OS reload as well as the new root/admin password. Be sure to copy this down! Please allow up to 10 minutes for the VPS to complete OS reload.
During this process, your VPS will show offline. It will show online as soon as the server is available.