Ssh in, get a root shell (sudo -s), and use your favorite editor to add

Listen 8080

to /etc/apache2/ports.conf. Replace 8080 with whichever port you need.

Note that links from the administrative interface to the application will still point to port 80; thus, depending on what you are trying to achieve, they may fail.

We haven't extensively tested this. Please let us know how it works for you.

is there anyway to change the port that the webserver runs on?