The smart move is once everything you want is backed up from the drive wipe C clean and install the 64bit fresh! You don't really have any upgrade path from 32bit anything to 64bit anything! The switch automatically calls for a clean install of Windows. Clean Install Windows 7
Here a fast wipe when booting live from GParted on flash drive if not disk or simply opening up the command prompt option when booted from a 7 USB Install Key to run the DiskPart tool and clean command and then see a fresh primary created is seen to when making any OS changes. Since you won't be able to use the WET tool(Windows Easy Transfer) between the two platforms you have to plan everything out fresh from the basic start off.