If you have a copy of the Service Manual, it will be helpful to print out pages INT13 - INT18 (Body Interior). This information can be used to remove the two pieces on the door so you can get to the screws underneath and ultimately remove the door panel. I followed the directions in the INT manual. You really need a thin tool for the bottom piece. One you get the two pieces off, then disconnect the wiring connector for the door lock / power window. Then remove the two screws.
Then use the wider tool to remove the clips around the outside of the door. There's 9 clips on the front and 8 clips on the rear doors.
Once you get the door panel off, check out the factory stock speaker. There are 3 screws holding it to the door and one wiring connector to disconnect. Then you can remove the speaker. My speaker harness wiring connectors didn't fit the Leaf, so I cut off the connectors and soldered / shrink tubed two speaker wires with connectors onto the car's speaker's wiring.
By the way, the Nissan Service Manual wiring color chart is incorrect for the Leaf.
Here are the colors I found:
Front Left (+) Blue / Grey
Front Left (-) Violet
Front Right (+) Red / Grey
Front Right (-) Brown / Grey
Rear Left (+) Violet / Grey
Rear Left (-) Light Green / Grey
Rear Right (+) Light Green / Grey
Rear Right (-) Pink / Grey
On the fifth photo down, you can see the rubber strips on the inside of the door that I had started to apply. I'll do some more testing and listening over the next few days to see if I can tell a difference with the rubber strips installed. It does feel more substantial in the door with the strips applied.