One of the straight forward (and not recommended) way is to configure the read/write permission on a folder within IIS.
https://www.webwiz.co.uk/kb/asp-tutorials/server-permissions.htm
However, what I would recommend to is to build a web service (ASMX, Web API etc.) on your web server to support read and write operations.
What you would do it then just pass the binary data to this web service and it will make sure to write the file on a specific location on server.
There are enough examples of this on internet. For e.g.:
http://stackoverflow.com/questions/16175004/how-to-read-a-text-file-with-a-web-service