I'm accessing mine using ssh with no problems at all. I've also transferred files to/from it at a distance using scp.
I suspect the problem is that you haven't forwarded the appropriate ports on your router, so the outside world has no access to your NAS at all.
If you're trying to access it on 192.168.x.xx then the above is definitely the case. You need to connect to your router's external IP address, after telling the router to forward whatever ports you wish to the NAS.
If you don't know what "port forward" means, type it into google.