First, do a backup of the profile. I presume that is at c:\users\<yourid>\appdata\roaming\thunderbird You should be able to upgrade over what you have, although the profile may be somewhat incompatible, depending on how old it is. The generally suggested approach is to upgrade to the first of each release to get up to date, such as in this link: https://www.thunderbird.net/en-US/thunderbird/releases/ e.g., 78.0.1, 91.0.1, 102.0.1. Your accounts, messages, and addressbook should remain intact. If you do follow the staged upgrade, I further suggest doing a backup as identified above after each upgrade to minimize any problems.