A lot of homes in America still use these vintage brass sprinklers they are superior to plastic ones although there are different types they all follow the same principle of disassembling.
Step 1: Removing
Clear any obstructions around you first, then with a pipe wrench and cheater start unscrewing it, it takes a lot of force
Step 2: Taking Out the Sprinkler
Before completely unscrewing the sprinkler dig out the surrounding dirt to make sure nothing can fall into pipe
Step 3: Disassembling
Will using the crescent wrench on the top use a pipe wrench below and unscrew the top
Step 4: Remove the Nut
Remove the limiter screw with socket
Step 5: Cleaning
Clean the parts however you want just make sure you remove as much junk as you can I used a pick and a file the surface doesn't have to be shining as long as you remove the stuff that was blocking flow of water.
Step 6: Back Together
Apply plumbers tape to the pipe, screw it one hand tight then then tighten with wrench and angle the stream of water