You can only from ‘beta’ or ‘tests-passed’ to ‘stable’ on the same minor release or higher.
So you can go from 2.3.x.betaX to latest stable (2.3.8), but not from 2.4.0.betaX because there is no stable release with a 2.4.x version number yet.
If you’re on 2.4.0.beta you need to wait until 2.4.0 stable is released (I guess in a few weeks from now) and then switch to stable. Make sure you don’t accidentally update before switching the branches because you will end up at 2.5.0.beta1 and you will need to wait for another 5 or 6 months!