How do you change the lower rear bumper trim panel?

I have installed a 328i exhaust on my 320i and I need to replace the lower bumper rear trim panel with one that has a larger opening for the twin tips of the exhaust.

I have tried in vain to look for this tutorial online but there doesn't seem to be anything on how to change this particular panel.

You would look this up for a 328i from 1995/96, as the chassis for this model is the same as the one I have.