There's a very good chance that this will be more of a pain in the ass than it's worth, and end up costing you a good chunk of change to boot. Unless your frame is steel, you won't be able to open up the rear end enough to get the spacing in. If your frame is steel, you can take it to a top-shelf bike store and have them "cold set" it for you (you DO NOT want to watch them do this!). Unless your frame is a nice one, this is likely not worth what it'll cost you. Then you'll need to replace the hub & freewheel body, shifters, and possibly the derailleurs. Might need to re-dish the wheel, too.
I'd be inclined to leave it as it is, and save up for a new ride. Keep this one around as a beater, 'cross bike, or turn it into a fixie.
<If you're gonna be dumb, you gotta be tough>
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