Hi, can any one please tell me , how can i implement a Windows form application that can upload a large files (average 10 Mb ) to the server. Secondly, please tell me what is the most efficient way to do so.

implement a FTP client-server application. there are lots of example on the web about how to do this:
http://www.codeguru.com/csharp/csharp/cs_internet/desktopapplications/article.php/c13163/

http://www.codeproject.com/KB/dotnet/dotnetftp.aspx

you can also use an existing ftp server that will reside on the server and you'll only need to write the client application that connects to that server:
http://www.codeproject.com/KB/IP/ftplib.aspx

implement a FTP client-server application. there are lots of example on the web about how to do this:
http://www.codeguru.com/csharp/csharp/cs_internet/desktopapplications/article.php/c13163/

http://www.codeproject.com/KB/dotnet/dotnetftp.aspx

you can also use an existing ftp server that will reside on the server and you'll only need to write the client application that connects to that server:
http://www.codeproject.com/KB/IP/ftplib.aspx