Its very easy to do. Just go into BIOS and set your computer to boot to your usb drive. Make sure your usb is inserted. During the installation of windows, you can wipe your hard drive. Just select custom instead of upgrade. Then click drive options and delete every partition until you get : Drive 0 unallocated space. Then select that drive to install windows on. Make sure the next time your computer reboots that you remove your usb drive or set BIOS to boot from your hard drive. This is because if you dont it will just keep booting off your usb.