You can reboot your server via the Hosting platform, see guide below. But this will only work if you server is online and able to accept a command. It is always best to try that option first for a nice clean reboot. If however you server has crashed and it is completely inaccessible, it will need a forced reboot.
Forced reboots are done via your client area login. Once logged in, select the server that is down from the list of services.
Select Manage VM
Then click Force Reboot VM