I don't think you can change the synchronisation path for files which are already in the Briefcase. You need to use the option to "Split From Original", delete the files and then drag files from the new server into the Briefcase.
OnePlus 5T review: Hands-on
Illustrator Andrés Lozano on his improv line work, brazen use of colours & hand sketching
iPhone X review
Comment envoyer gratuitement des gros fichiers ?