Hi, First off. If you intend to move to the 64 bit version of Win 7, then you will have to do an clean install of Win 7 64 bit,as you cant do an upgrade from 32bit to 64 bit. As for your software, the product key is for your dell 32 bit version of Win 7. The retail version of Win 7 comes with the 32 bit and 64 bit disc's , where the product key is good for both versions, but not the OEM (Dell) version, that will require an product key for each version. If your Vista came with 32 bit version, then Dell will only supply an 32 bit version of Win 7.
I received free upgrade offer of Windows 7 Home Premium with my DELL Studio 1555 laptop which originally had Windows Vista Home Premium, both 32 bit versions. I have activated the Windows 7 32 bit product key and is working fine. This laptop has 4 GB RAM and Windows 7 32 bit is recognizing only 3 GB. To make use of this additional 1 GB of RAM I am planning to switch to Windows 7 Home Premium 64 bit version from 32 bit version. Is it ok to use the current (32 bit upgrade) product key and activate Windows 7 64 bit version in the same laptop or do I have to buy Windows 7 Home Premium 64 bit upgrade product key ? How can I get access to 64 bit Windows 7 Upgrade disk ?
Switch From Windows 7 Home Premium 32 bit upgrade version to Windows 7 Home 
Premium 64 bit version