Hi pastit,
When i did mine only one shroud came out, the O ring had dried up in it and stuck like glue.
I removed the injector from it by spraying penetrating oil in the shroud, left it a couple of hours, and then got the injector to turn in the shroud. Once it was turning it came out easily.
I removed the other shrouds to give them a good clean anyway, don't forget to seat them properly when you put them back in, a bit of lube will help them just CLICK back in place.
Hope you get sorted.
