Welcome to LQ!
There are a couple of ways how to deploy applications on JBoss. Here you can get an impress:
http://community.jboss.org/wiki/JBossAdminGuide
Usually you don't exchange "a couple of html files" in applications running on JBoss or other application containers. You deploy them by placing a new application archive (.war, .ear
,...) and tell the server admin tool to deploy it. So maybe your customers simply have to give you a new .war-file that you deploy on the test site and if test is positive you shift it to the live version?
The database is a different topic. What database server is used? For MySQL i. E. there is a web admin tool call phpMyAdmin. You can use that for free and grant different users appropiate access.
www.phpmyadmin.net
For PostGresql
http://phppgadmin.sourceforge.net