You could easily have gotten an answer using Google. Google is excellent. You should use it. [URL]#
My Latitude E6420 shipped with Windows 7 Ultimate 32 bit.  I have the 64 bit reinstallation media from Dell.  I can't find any instructions on how to upgrade to the 64 bit version and Dell has offered to sell me the instructions - basically I have to purchase a software support contract for one year. Does anyone have the instructions on how to upgrade to 64 bit or do a clean installation from the 64 bit reinstallation media?  Tried booting with the media in the drive, using F12 to boot from CD/DVD drive and using F8 to boot and none of these options worked.  Get an error message that the version on the CD is not compatible with the version I'm running.  
Upgrade Windows 7 Ultimate from 32 Bit to 64 Bit