I was unable to obtain any error reports from the server as I am running the site from a hosted service who do not like passing them on!
After many attempts I finally figured it out.
You have to remove/uninstall the old version and then install the new one. So at least now I am up to date.

Hi,

Sorry I thought I made that clear in my initial post, nothing works.
The Upgrade page, the module management, nothing.

Hello,

I recently purchased a copy of JoomSEO but when I attempt to update from the free version I was trying (Version 4.0.9) I get this error on a blank page

The website cannot display the page HTTP 500

This happens if I download the zip file via your e-shop link, or use the Online Upgrade to Paid Version button or even use the Extension manager to upgrade or install the zip file. Nothing works. Apart from your site charging me €26.90
Can someone tell me why please?