Replacing shackles

I am replacing the shackles on my 2001 sierra and I have a couple of questions. The instructions that came with the new shackles say:

1. Raise the vehicle with a jack using the pumkin.
2. Remove the shocks lower bolt and remove the bottom of them.
3. Lower the vehicle.
4. Remove both the uppeer and lower bolts on the shackles.
5. Replace with new shackles.
6. Raise vehicle and re-attach shocks.

Here is my problem, I was able to remove the old shackles, and attach the new ones to the spring, but I cannot get the spring lowered again.

Should I be removing the spring completly? Or sould I be removing the U bolts and some shims?

Any ideas would be great