How to Copy or transfer from NAS to NAS over the internet?

[FreedomPirate01]

Hello, I have a 219P in NY and a 119P in Poland and I would like to copy over everything on the 219P or atleast certain folders to my 119P. Both NAS devices have high speed net and are connected via Airport Extreme. What would be the best way to go about this and where can i find step by step instructions. Thanks!