C++, c# file transfer

I have a client server program that needs one method rewritten. The server application is written in c++ and the client is written in c#. The purpose of the applications is to transfer files from on computer to another computer without the need for FTP. The application uses winsock for the connection between client and server. The current method is too slow to keep up with the volume of files that are being sent. To test the application the server application must be run on a slower computer and the client on a faster computer. It is one method and must send the file as quick and efficient as possible from the client c# application to the server c++ application. I have a working project but a I mentioned it is way too slow for a production environment. Thanks and good luck bidding.