Texture Slideshow

My app has a long conference-room scene where we do a slideshow on a screen mounted on a wall. When I wrote this a while back, I used a decal as it was the easiest thing for me to do at the time. Now I need to determine the "right" way to do it... I'm sure I've run across something like this in the forums, but my brain can't seem to formulate a relevant search mask.

Bascially, I need to be able to swap out the image, on demand, without the texture hanging around in memory like it currently does.