Amazon sells the upgrade for about 170 Dollar, but i am sure there are cheaper ways. If you have a valid license of Win 7 32 bit, you might approach your distributor if you cannot change this to 64 bit. I believe the Pro License shall include both licenses 32 bit and 64 bit doesnt it ?

http://www.amazon.com/Microsoft-Windows-7-Professional-Upgrade/dp/B002DHGM50

 

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