Do not try to remove the head under pressure. It is possible that some water may be in the line and come out when you remove the head, but it is not under pressure. Dig around the head, carefully so as not to break the PVC pipe, and when you get the dirt cleared away, you will see the head just screws into a fitting. Most likely this will be on the end of a "funny pipe" which is just a somewhat flexible plastic pipe that transitions between the main PVC line and the head that allows the head to be set to the proper level easily and to prevent breaking the head or fittings is it is stepped on. The head could be screwed directly into the PVC line, but no matter how the head is connected, it is just screwed on. You may need a pair of channel lock pliers or a small pipe wrench to unscrew the head, but try if with just your hand first. These do not have to be torqued down, hand tight is really adequate. Also, no pipe compound, Teflon tape or other sealer should be used when reinstalling the head. If you need some more reassurance, just go to the irrigation supply store and look at the head. It's really very simple.