pressure regulator backflow valve

[Seawulff]

Any suggestions on how to install a Zurn pressure regulator backflow valve in this location? I upgraded from a manual fill process to an auto fill and this old sprinkler valve leaks.
I'm not sure how to get this off without breaking the wall or pipe and then I'll be in deeper trouble!
Thanks

 

[JamesW]

Probably need to cut the pipe and use a coupling to put it back together.