Possible Duplicate:
How to upgrade from Windows 7 x86 to Windows 7 x64?
What's the [best] process to upgrade a computer from Win 7 x86 to Win 7 x64?
Possible Duplicate:
How to upgrade from Windows 7 x86 to Windows 7 x64?
What's the [best] process to upgrade a computer from Win 7 x86 to Win 7 x64?
While there is no direct upgrade path across architectures, you can use Windows Easy Transfer on the 32-bit machine to transfer all of your files and settings to the 64-bit machine.
You should remove old 32bit and install new 64bit version of Windows 7 in your system.