Click on the Mount button ISO is mounted to your server. Next you need to change the boot device and reboot your VPS.
Click on the Settings tab
Select '(1) CDRom (2) Hard Disk' from the Boot Order drop down list
Reboot your VPS by clicking Reboot button
Please do not forget to change the Boot Order value back to '(1) Hard Disk (2) CDRom' to boot from the hard drive after you finish working with the ISO