All you need is a cloud storage (because you are not sure of whether to use 4Shared or MediaFire). You can look for other options, I have used
Dropbox API[
^], which was convenient for me a lot.
C# is a programming language, not a software application to connect to services and upload files. You require packages, namespaces and libraries to make C# work the way you want it to. For 4shared, please read their developer guides and learn more about their API at:
http://www.4shared.com/developer/[
^]
MediaFire is same, you just need access to their API to be used in your C# application. Their API and developer guides are listed at:
https://www.mediafire.com/developers/[
^]. The process is same, read the documentation for guide for developers, register yourself as developer, register your application and follow the steps to integrate the API in your own C# application. They would have a source code example for you already there. :)