Well, I believe that Partition Magic could do this under certain circumstances, but I doubt that your situation fits them. PM can reduce the 50 down to 10, leaving 40GB of unused space. And it could add 40GB of unused space onto the 10, if it were adjacent. However, you probably have two partitions, the first one 10 and the second 50, so after reducing the fifty, you'd have 10/10/40, and you'd want to add the 40 onto the first 10, which it can't do.
I'd say that it would be easier to just reinstall, especially since you just did it and don't have too much to redo. I usually end up reinstalling 3 or 4 times every time, just because of doing stupid things like that.
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Bitt Faulk