I suggest one of the following approaches:
a) get rid of the separate files at the sub offices. Set them up to access the same database as your Head-Office. Then you will not have any discrepancies in your data. Unless you contract with a FileMaker Hosting service, you'll need to either figure out "port forwarding" or hire a knowledgeable person to set it up for you so that your sub offices can access the database through a port opened in the firewall that enables this access.
b) there are "synch" tools for FileMaker Go and Filemaker Pro produced by third party developers such as 360Works and SeedCode. The SeedCode tool at least, don't know about 360Work's version, can synch either FileMaker Pro or FileMaker GO files. Synching data without losing data is not a simple thing to set up so having an expert do it for you makes a lot of sense though it will cost you some $$ you wont' have to spend if you develop this for yourself.