When changing ports, You must do it on server, then adjust port forwarding on router, and finally modify, on which port Your client tries to connect.

I strongly encourage You to use VNC over SSH tunnel - now, Your data - including passwords - is sent "almost" in the clear.

Personally, I also keep away from standard ports - it KO script kiddies out, and even a little more advanced tools get problems with identifying services used by open ports. Not to mention, that many tools by default scan only first few thousands of ports (so, using one from out of this range, help again to keep script kiddies out).

/Estel