The device at the top of the tall pipes is a vacuum breaker. It's purpose is to keep your drinking water from getting contaminated with soil bacteria and pesticides. It has to be set at least one foot higher than the highest sprinkler head orifice in order to work. If you set it lower than that, it will back flush sprinkler water into your fresh water supply. So, unless you want amoebic dysentary or a good case of typhus, you should either leave it alone or replace it with a "double check valve", which does the same thing but can be placed in a meter box underground. They cost about 80$ at Home Depot. Just follow the piping into the ground, dig a hole big enough for a large square meter box, and install the double check in line. For that size area, you need a 3/4" double check.

The other device on the slighty lower above ground pipe with the wires is a sprinkler remote control valve, why some idiot put it on a riser is beyond me, just drop it in the ground and put a round valve box over it.