Honestly it wouldn't be worth it, you would be better off spending the money on a new bike. First off you would need a new rear hub, new cassette, new derailleur and shifters. On top of that I believe the spacing for the rear hub would be different so you would need the dropouts spread apart.
Once you look at doing that upgrade and replacing your fork you could have already purchased a new bike.
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I may be fat but I'm slow enough to make up for it.