www.kennel-kees.dk seems to be gpEasy 3.5.2.
You could try the following steps to manually update the site to the current Typesetter version (ideally to 5.1.1-b1), with the ability to roll back, in case it won't work this easy way:
- Download the current master (Typesetter 5.1.1-b1) from GitHub
- Extract the ZIP archive to your local computer
- Make a copy of the extracted /inlude directory and name it /include511b1
- Copy the whole /include511b1 directory to the webserver
- When done, rename the old /include directory on the server to /include352
- Rename /include511b1 to /include
- See if it works. If not, you can just roll back to 3.5.2 by reverting the names of the /include* dirs
You may also need to replace /gpconfig.php on the webserver with the new version.
Same might apply to /.htaccess. If you replace /.htaccess, you'll need to make it writable to PHP to re-enable URL-rewriting via Configuration->Settings->Permalinks