I have low water pressure on my rainbird sprinkler system. how can i adjust it?

There are several ways to adjust water pressure on sprinkler systems. First you have to determine if there is a problem with the sprinkler system itself. Things to look for:
1.) make sure that all valves including the main are all the way open.
2.) Inspect the sprinkler heads for clogging. Sediment and debris can also clog your sprinkler heads. Some debris removal may be required.
3.) You make have too many sprinklers operating by one valve. You may need to divide a zone and add another valve to increase water pressure.
4.) If all else fails. You can install a breather intake cap to allow air into your sprinkler system thus increasing GPM (gallon per minute)flow.
5.) one of the biggest mistakes that peopel make is that they undersize the water pipe size to save money. Typically you want to use 3/4" PVC pipe for your main runs and tee into 1/2" PVC for your sprinkler heads.
Good luck. I hope this helps.