Updating the app’s version number

The default version number of the app is 1.0.0.
To update it, navigate to the pubspec.yaml file
and update the following line:

version: 1.0.0+1

The version number is three numbers separated by dots,
such as 1.0.0 in the example above, followed by an optional
build number such as 1 in the example above, separated by a +.

Both the version and the build number may be overridden in Flutter’s
build by specifying --build-name and --build-number, respectively.

In Android, build-name is used as versionName while
build-number used as versionCode. For more information,
see Version your app in the Android documentation.

When you rebuild the app for Android, any updates in the version number
from the pubspec file will update the versionName and versionCode 
in the local.properties file.

Android release FAQ