Decompile exe and dat file

I need this files to be decompilte to retreive the source code. The full source code may not need to be fully retrieve but i need it to be modify to suite my requirements. The GPSSVR is an GPS tracking application which works as a port listener and convert the HEX protocol to ASCII before inserting into the DB. I need to add on more protocol to support other different GPS devices. I need you to get the working principle of the GPSSVR and create another working application with new protocol. The second file is a dat file which contains some data on domain name and features. I need it to be decompile and replace the domain name with another and change the features files in it. It needs to be recompile back into dat file for other application to work.