Changing settings on files already published online

I have published a 15-part magazine series online, protected by a paywall. Publishing each issue online was without problems and I know how to publish InDesign files using the Publish Online dialogue box. At the time I did NOT allow subscribers to download the magazines. They had to be read online using their password.

However, I am going to close the website and delete all the files, but I want all paid subscribers to be able to download the files first.

Am I able to change the preferences to allow subscribers to download the files, and if so, how dod I do that?

Or, do I have to republish all the magazines, allowing them to be downloaded, and delete the original files? This seems like a slow process, compared with being able to just change the preference on a file already uploaded.

I have looked at the Publish Online Dashboard, and can see all the files, but can't see any way to change the preferences.

Thanks in advance.