If you're using ver 102, then there is a menu item, tools>export that will create a backup copy of your full profile. If you are on older version, then do this: - click help>moretroubleshootinginformation and scroll down to Profile folder and click 'open folder'. This is to check exact location of profile on PC. - exit Thunderbird (important) - copy the profile to a USB stick or other portable device. if win 7 layout is similar to windows 10, the location is something like c:\users\<yourID>\appdata\roaming\thunderbird\profiles\<profilename>

After update, - install new thunderbird first - start thunderbird, ignore email wizard, click home tab, on that screen click 'import' and from next screen select the profile you copied from old pc. And you're done.