Supposedly you can download the .ISO file and burn your own DVD.
http://techpp.com/2009/11/11/download-windows-7-iso-official-direct-download-links/
You will have to do a clean install of the 64-bit version as there is absolutely no "upgrade" from 32-bit to 64-bit.
See info @
http://windows.microsoft.com/en-US/windows7/Installing-and-reinstalling-Windows-7
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