Help menu (Alt+H) > about and read what it says.

Or

Help Menu > troubleshooting information and look at the application basics section.

it says 52 50 I read thw latest is 5252....how do i update it ??

To Update Thunderbird

By default, Thunderbird is set to automatically update itself but you can always do a manual update. Here's how:

1. Go over to the Help menu and select About Thunderbird. The About Thunderbird window will open and Thunderbird will begin checking for updates and downloading them automatically.

2. When the updates are ready to be installed, click Restart Thunderbird to Update.

This info came from:

https://support.mozilla.org/en-US/kb/updating-thunderbird

I've moved this thread to Thunderbird support since this is a question about Thunderbird and not about Firefox.

Robert.Myers said

it says 52 50 I read thw latest is 5252....how do i update it ??

While you are on the About screen there is a big button offering you an update or saying Check for Updates. Is yours missing or did you just overlook it?