I will explain the fastest and simpelest way to install an operating system of your choice on an ovh server.
Go to your dedicated server on the ovh manager, go to services (diensten).
go to net boot, select vKVM, reboot your server via the manager.
You will get an login/password by mail from ovh and how to login.
the adress u need to go is:
login with: kvm
and the password u got from ovh.
there u can mount iso files from ftp servers.
have fun installing your new operating system
(dont forget to install rdp, vnc or ssh to the server or u wont be able to access the server remotely.)