It's pretty simple if you can install an e-clip <- pointing to my difficulties with same.
You can do the change without the helper rod, but I've worked on enough weapons with spring loaded parts that I included it anyway.
1. Unload the weapon
2. Rack the bolt carriers to clear the chamber
3. Pointing in a safe direction pull the trigger and release the striker
4. Remove the rear cover
5. Remove the bolt carrier, striker, bolt and bolt lock
6. Find the sear, and sear pin e-clip - note the position of the e-clip (how far it's pressed on the pin)
7. Remove the sear pin e-clip
8. With a rod a little smaller than the sear pin, inserting the rod from the left side of the receiver, push the sear pin out to the right side
9. Withdraw the sear and the safety spacer from the rod and get ready to use the rod on the trigger pin in the same way
10. Find the trigger pin, and e-clip thereon - note the position of the e-clip (how far it's pressed on the pin)
11. Remove the e-clip
12. Push the trigger pin out of the receiver to the right just like the sear pin.
13. Take the new trigger/disconnector assembly and insert it into the receiver - you may have to gently manipulate it into place
14. Fun part #1 - replace the e-clip on the trigger pin. MAKE SURE IT IS FULLY ENGAGED WITH THE TRIGGER PIN!
15. Check the sear striker stop surface for burrs from machining, if there are any, hit the edge gently with some 600 grit wet/dry DON'T ROUND THE EDGE!
16. Put the rod far enough into the receiver that you can slip the new sear onto it, and holding the sear spring down with the new sear, insert it into the new sear
17. Check that the safety has not "walked" out to the right - if so push it back in - you won't be able to install the sear if it has
18. From the right side of the receiver, reinsert the sear pin by pushing the rod to the left out of the sear. You'll need to push down on the sear somewhat to get the pin aligned on the left side.
19. The fun part - put the e-clip back on the sear pin. MAKE SURE IT'S FULLY ENGAGED!
20. Check the function of the trigger by holding the sear as if the striker were captured and see if it releases when the safety is in fire position, and will not release when the safety is in safe.
21. Reassemble the bolt grouip and check the function by racking the bolt carrier and trying the safety tests again.
22. If it passes you are ready to rock and roll!