Git Bash
Note, if you are instead looking to find out what version of Git Bash you are running, or want to see if you need to update Git Bash, it is part of Git for Windows.
So your Git Bash version is:
git --version
git version 2.23.0.windows.1
Note that it is technically different from Bash. On my same machine when I run:
echo $BASH_VERSION
4.4.23(1)-release
Git for Windows installer
To update to the latest version of Git and Git Bash, you can download and install the latest version of Git for Windows. As per this FAQ, settings/customizations should be preserved if they were installed in the appropriate configuration folders.
Note: Their installer is actually intelligently designed to do the right thing (though it doesn't tell you upfront that it defaults to your prior settings automatically!).
If you are doing an update, then every screen on the installer is pre-marked with the settings from your current (soon to be previous) install.
It is not showing you generic default settings. You do not need to look any of them up, or fear for breaking your carefully honed setup. Just leave everything as is, to retain your previous choices.
In fact, they made it even easier (if only it was clear that they did so).
There is a checkbox at the bottom [] Show only new settings (I don't remember the exact wording). Since nothing on the first screen changes when you mark the box, it is not exactly obvious what it is for. If you mark the box, then all of your current settings will be retained, and it will skip showing those (subsequent) settings screens to you. Only screens with newly introduced settings will be shown.
git update-git-for-windows
Alternatively, as others have noted, you can also update Git Bash and Git (by definition, both are always updated at the same time) from the Git Bash command line, via:
git update-git-for-windows
If you type git update, Git kindly reminds you that the command has been updated to git update-git-for-windows:
Warning! git update has been deprecated;
Please use git update-git-for-windows instead.
Git for Windows 2.26.0.windows.1 (64bit)
Up to date