What is the best way to make Web Access available on a public ip address?
If you want Web Access to be publicly accessible, all you'll need to sort out is how to connect to your web server from outside of your network. That being said, there are several important details to consider, including security (and, by extension, firewall/DMZ configuration), whether ports are forwarded correctly, and whether or not you'll need to set up a static ip or domain name. The Web Access Administration help files discuss some of this, but the rest falls outside of the purview of Laserfiche, so there's little else we can do to help. There are lots of guides online that discuss port forwarding, firewall configuration, and IP/domain name configuration, but without more information about your situation, I can't make any recommendations.
The best way is the secure way. You can put the web server on a public address without any changes but it is not secure by default.
Create an A record in your public DNS that will be used both to resolve to the public IP and as the friendly name on your SSL certificate.
In IIS setup a 443 binding with an SSL security certificate. Then configure the website to require SSL and create a forwarder listening on port 80 to forward to the 443 port.
In detail:
http://www.iis.net/learn/manage/configuring-security/how-to-set-up-ssl-on-iis
Most SSL providers offer free help configuring SSL on your IIS server.