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.
How to install OS
Power down the virtual machine first.
Click ISO.Select your ISO in drop-down Image Name menu, and click OK.It will appear in the Virtual disks list.Then start VM.And click VNC.You should see boot menu of your ISO:
Windows installation from ISO
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%)