pdabrowski
The recommended (& only procedure I believe), is to do a backup to attached USB (from console for easiness), then do a fresh install of the 64 bit software to your existing hardware making sure to erase & overwrite the existing 32 bit install.
At first boot you will be asked to attach the USB backup disk & you can then do a restore from backup.
Wait until asked BEFORE connecting the USB drive.
Then reinstall any contribs & other manual tweaks you have made.
If you have a RAID array then you might like to put one disk aside in case of problems you can revert to the old 32 bit install.