You need to enable remote access via what ever method you choose, in the server-manager look under Remote Management. If you want to access it over a VPN you can use the Windows VPN client, but you'll have to enable at least 1 PPTP client & forward the appropriate port in you router to your server, (port 1723 + GRE).
If you wish you can tunnel over SSH to your server, to do that you'll have to enable public secure shell access over what ever port you choose, (I suggest that you don't use port 22 for security reasons) & forward that port to your server in the router. Instructions on how to set up a SSH tunnel using Putty can be found here,
http://martybugs.net/smoothwall/puttyvnc.cgi. Just ignore the bits about smoothwall & VNC as required.
There are other solutions including this one,
http://3sp.com/showSslExplorer.do.
HTH
Peter