By Right click on the disk oe volume down there you'll get a context menus - you should be able to remove any current patition and then create new one. You might get prompted to Initialize disk as well. If you'll get lost you use the Windows built in help - it's failry easy to follow.
As said before - if you're planning to use it as external storage for Windows only just right click on the "Computer" link in the start menu and Select Manage - this will open the Computer Management tool window, then go to Storage, Disk management. You should see your disk there (in the bottom section only), just be sure to find the USB one and not to wipe the internal one of your PC / Laptop.