I keep getting this message but do not have away to change the URL from BOINC manager. Is there a way to fix this. I can't delete it either.

GPUGRID: Notice from BOINC
This project is using an old URL. When convenient, remove the project, then add https://www.gpugrid.net/
5/21/2020 1:25:39 PM

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I think their servers are down at the moment. When they come back up, you will be able to detach from GPUGrid and start over.
You can just add the "s" to the address in the BOINC Manager window as the easiest way.

Servers are back up, and new work is flowing. One or two glitches along the way - we may yet find more - but I think they're ready for you to do what they suggest: when convenient (when you have no tasks at all from the project, using 'no new tasks' if needed), just detach and re-attach.

reattaching the project just adds the old link.
That being said, both old and new link show the same data (with or without 's').
Boinc Bam Stats doesn't show any difference in project address, so adding it to BAM, will automatically get you the old address (without 's').

No, it doesn't. Reattaching via BOINC Manager is different.

1) The url data box is editable - you can add the extra 's' if it makes you feel better, but if it can find any part of the project, it makes no difference.
2) All the supplied url does is invoke

http://www.gpugrid.net/get_project_config.php (note no 's' in this test)

which will attach you to

<master_url>https://www.gpugrid.net/</master_url> (with an 's')

And once you've done that, the warning messages go away. At least, they've gone away on all my 7 GPU machines.