If you're talking about changing the patterns on a TA, there's dip switches on the back of the controller. One of them (I believe far right) is the "flash" flash pattern, down is the double sweep only (like the top) and up alternates between the 3 (like the bottom). The others control the patterns of the arrows, and one of them switches between a 6-head unit and an 8-head unit. Whelen has a PDF that details the switches.
There are different models, some have 4 dip switches and some have 5. This may or not be the particular control head you have: