I have uninstalled the roon software from my pc, downloaded and installed the production version, but as you can see from the screenshot, I’ve still got the early access version.
Your screenshot is of your Nucleus’s Web Administration Interface - and that is where your Early Access Roon Server is running. Please read the section of the article I quoted that gives instructions (and a file to be downloaded) for restoring the Production version of Roon Server on a Nucleus.
Use Windows File Explorer to copy it across to \\Nucleus\Data\Reinstall For example, I have a ROCK/NUC system, so I would use \\ROCK\Data\Reinstall in File Explorer…