The zoom effect used on the Recycle Theme main slider is called the “Ken Burns” effect. It gives action to still images by slowly zooming in on subjects of interest. It’s a nice technique to use when there is no video material available, but it can be quite resource intensive.
To disable Ken Burns zoom, navigate to the Slide Editor and under the Main Background settings locate the Ken Burns tab. You’ll find here a couple of options to alter the behaviour of the zoom effect, but if you want to get rid of it completely, simply switch it off using the blue button on the top of the settings.