Hello. I have an old HP Z400 workstation that I recently obtained. It came with Windows 7 professional OA 32 bit. I recently purchased 20gb of ram to upgrade and of course need to go 64 bit to take advantage of the ram. I have the official windows 7 pro 32 bit, and 64 bit CDs I previously bought so thought I could just put the 64 bit CD in and upgrade... Nope. I will have to check if the HP recovery CD is still around somewhere, but was most likely tossed unfortunately. I have heard that there may be a way to download an ISO to perform the upgrade, but have also heard that this may not work with a preinstalled OA version even though this is a validated licensed windows 7 with COA sticker, etc. Any advice/help would be appreciated! I also thought about simply upgrading to 10 64 bit, but not sure that will even work due to this being OA. Thanks.