For such moves, although technically not required, I always suggest making a copy of the profile. To do that, - click help>troubleshootinginformation - scroll down to 'profile folder' and click 'open folder - exit thunderbird (IMPORTANT) - you are now in the profile, back up three times in File Explorer and then copy the folder named Thunderbird to somewhere else. - now start and uninstall the 32-bit version. At end, it may prompt on whether to delete data folders. DO NOT ALLOW. - now install the 64-bit version and it should be okay, as all settings are in the profile, not the software.