5.4b is the latest official release. 5.0E is likely an intermediate version that was on your Audya 4 when new which is normal. It is not available for download on the website.

You will need to install 5.3D before installing 5.4B

5.3D:
https://www.ketron.it/en/software/53-audya-4/audya4-5-3d

5.4B:
https://www.ketron.it/en/software/53-audya-4/audya4-5-4b