Depending on the style of sprinkler head, most heads that have quit rotating need to be replaced. If it is early in the sprinkler season you can try to back flush the offending head by stepping straight down on it while it is in operation. If the issue happens to be some post-winter debris this can flush out the head. Much like humans, sprinkler heads get tired over time and the rotation gear just wears out. 

The impact rotor, the Maxi Paw, does have an adjustment under the nozzle that can help restore rotation. It isn't always 100% effective and may last a couple days or an entire watering season, but it is worth a shot if you have Maxi-Paws. Check the Maxi-Paw article here.