The first thing you would need to do is back up all the data. Any way you're going to do it, you're going to end up wiping out all the drives. My recommendation would be to purchase an external hard drive that's at least 500GB in size and back up all important data to it.
After that is done, re-install Windows like you want. NOTE: You can't extend the C: drive onto other disks without a 3rd-party utility.
After Windows is done installing, follow these steps on the 2nd-4th drives: http://howto.cnet.com/8301-11310_39-57378002-285/how-to-turn-old-hard-drives-into-one-large-drive-in-windows/
You'll end up with 2 drives, C: and D:. C: will have the same amount of space it has now, and D: will have the rest. Personally, I prefer to have the drives separated like this and keep all my data on D:, so I can reformat Windows without losing anything important at any time.
IMPORTANT NOTE: If ANY of the drives in the spanned volume fail, you lose all data on them. Proceed at your own risk.