As your computer is a 64 bit this means you can use either Thunderbird win32 or win64. This means you are perfectly ok to continue using that 32bit version, but you can change if you prefer. The program itself would be installed in the same location, so you would need to uninstall 32 version before installing 64 version. Thunderbird program is automatically installed in the default location: * C:\Program Files (x86)\'''Mozilla Thunderbird ''' So if you want to uninstall, go to the above location and delete the 'Mozilla Thunderbird' folder. Obviously, Thunderbird would need to be closed first. Then empty the desktop 'Recycle bin'. The Thunderbird program is completely separate from the Thunderbird profiles which are stored in an entirely different location. Thunderbird profiles are stored here: * C:\Users\<Windows user name>\AppData\Roaming\Thunderbird\Profiles\'profile name' folder If you have not created a backup copy then it would be advisable to create one. Exit Thunderbird and go the above location and copy the 'Thunderbird' folder to a suitable location eg: external drive. You can also locate the profile via Thunderbird prior to closing Thunderbird. * Menu app icon > Help > Troubleshooting Information * Under 'Application Basics' section about 8th in list is 'Profile Folder' - click on the 'Open Folder' button. * Exit Thunderbird. * Go up the directory until you are in the 'Roaming' folder and then copy the 'Thunderbird' folder. Thunderbird can be downloaded from here: * https://www.thunderbird.net/en-US/thunderbird/all/ Additional information: * https://support.mozilla.org/en-US/kb/installing-thunderbird-windows