In so far as I know there is no way to upgrade from 32bit to 64bit Windows 7. Please refer to this article from Microsoft and read question number 5.
32-bit and 64-bit Windows: frequently asked questions
You need to backup everything and do a clean custom install.
If you only have upgrade media your options are limited as to how successful your attempts to clean install with upgrade media might be. You can refer to this article for further reference
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If you have the full retail version of the media then you need to backup all your critical data and start over with a clean install.
In either or both cases a clean install of windows 7 appears to be the only option available to get from 32bit to 64bit.