The kit comes with a lighter trigger spring, a lighter sear spring and a sear.
Refer to http://nwtownsends.smugmug.com/photos/238574776-XL.jpg
1. Use a punch to push the sear pin (11) to the right as your are looking down onto the frame. You don't have to push the pin all the way through. Just enough to let the striker safety lever (25), sear (10) and sear spring (13) fall out.
2. Insert the replacement sear. Refer to the photo for orientation. Push the sear pin in just enough to hold the sear. Install the sear spring into the sear. Push the sear pin in again to hold the sear spring in place.
3. You can fight with the sear spring to get it under the ejector pin (12) or use a flat blade screwdriver to push the ejector pin to the right. Again, you don't have to push it all the way through. With the ejector pin halfway out of the way, push the sear spring to the left then down and tuck it under the ejector pin. Push the ejector pin back into place.
4. Next, reinstall the safety striker lever. Refer to the photo for the orientation. You have to get the bottom side in first, then slide it to the rear of the frame, then the top part hooks up and back.
5. Push the sear pin back into place. You can use the punch or an Allen wrench to help line up the pieces. Make sure both the sear pin and ejector pin are not sticking out.
6. Next, rotate the take down lever to the 2:00 position. While pushing it from the right side of the frame, pull and turn the lever. Keep turning it and pulling gently. It will eventually work its way out.
7. Using a punch, push the locking block pins (5) through. Gently lift the locking block (4) up and out.
8. With the locking block out of the way, the trigger assembly will be accessible. Pull the trigger back slightly then up. The trigger (7), trigger bar (8) and trigger bar spring (9) will come out. Replace the trigger bar spring.
9. Reassembly is basically the reverse of what you just did. Replace the trigger assembly. Replace the locking block. Make sure the slide stop lever (18) goes under the slide stop lever spring (19). The slide stop lever spring should still be attached to the locking block.
10. Align the components and push the locking block pins back in. Replace the take down lever by rotating it and pushing in gently.
I hope this helps. It's really simple. If you can field strip your XD, you can do this mod.