You can remove Thunderbird through the Control Panel in the Start Menu on Windows, by removing the Thunderbird application on OS X, or by removing the thunderbird folder on Linux.

Removing Thunderbird won't remove your emails or newsgroup messages. This data is stored in your profile folder, which is located in one of the following locations depending on your operating system:

Windows Vista Users\<UserName>\AppData\Roaming\Thunderbird Windows 2000, XP, Server 2003 Documents and Settings\<UserName>\Application Data\Thunderbird Mac OS X ~/Library/Thunderbird Linux and Unix systems ~/.thunderbird

Any version of Thunderbird that you install after removing Thunderbird will continue to use the data from this profile folder.