Modifing Files on Remote Server

I am running into an interesting problem. I'm sure there is a way to do it, but i'm just not thinking of it.

I have an ASP.NET applications running on its own server. I also have Server A and Server B that are in different locations and not on the same network. I can access Server A and Server B by IP address.

Now I need to have my ASP.NET application to modify files that are located on either Server A or Server B.

I can impersonate my ASP.NET application as a user on each server, so permissions will not be an issue.

The problem I am trying to figure is; how do I connect to each of the other servers by only knowing the IP address? I would rather avoid going down the whole FTP route if at all possible.

Any ideas?