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Hunter is a very good brand and should help you with the selection of the sprinkler. Also a local irrigation supply store would do as well and should be knowledgeable about Hunter products. Most likely you would have to dig up the head to the threaded lateral waterline pipe tee-fitting. Unscrew the old irrigation head and screw in the new into the threaded tee. Match heights of the heads and use teflon tape on the threads on the new head before screwing it in. Take the nozzle off the irrigation head and flush the sprinkler for a few seconds and then replace the nozzle then adjust the spray reach and direction of the nozzle and your good to go. Aloha