You should use ddns, Services->Network, there are free DDNS servers out there.
Or if you want to remove all restrictions, edit /etc/httpd.conf and comment accordingly.
WARNING: the ALT-F webUI was not designed, nor audicted, with any but the most elementary security precautions, appropriate only for naive normal user attack attempts. This means that it might be susceptible to attacks, and you don't want to expose it to the internet.
Services provided by Alt-F, such as ftp or ssh, have their own security, BUT by default and for memory saving reasons, they are launched by inetd, which is know to be susceptible to attacks. If you want to expose those services to the internet you should launch them in server or standalone mode, not under inetd control.