To update the versions of all of the poms in a multiple module project use the versions-maven plugin.
$ mvn versions:set -DnewVersion=1.4.0-SNAPSHOT
Will modify all of the versions of each of the poms to the version specified. It will create a pom.xml.versionsBackup for each pom file that it modified. You can then examine each to make sure that it is as you intended.
If you want, you can revert your change with
$ mvn versions:revert
If you are satisfied with the change, you can commit the change with