You can install any other operating system on your machine for free. To do this, you only need an operating system image in the .iso format.
Please note that uploaded ISO stored only for 24h.
Windows
Disks: If the hard disk is not detected: to make windows "see the hard disk" you must add virtIO driver ISO in addition to windows ISO:
https://fedorapeople.org/groups/virt/virtio-win/direct-downloads/archive-virtio/virtio-win-0.1.141-1/virtio-win.iso (Install this driver: virtio-win-0.1.1/viostor/%OS%/%CPU%)
Network: You need to install network driver from the same virtIO disc and set up networking as noted in server's description.
How to install OS
Power down the virtual machine first.
Select Disks.
Click ISO.
Select your ISO in drop-down Image Name menu. Set boot priority "To the beginning" and click OK.
It will appear in the Virtual disks list.
Then start VM.
And click VNC.
Afterwards you'll see the boot menu of your ISO.