I've done this once or twice (on the older M646 version)
Take the black end plates off (4 bolts on each). The outside face of the pedal will then come off. I think it has a spring in it that makes the SPD pop up. It's a bit of a faff to put back in.
Once the end is off, there's a wee cap over the end where the bearings are. Remove it, and inject grease. You can roll the seal at the crank end of the axle to let old grease out.
I wouldn't take the axle and bearings out unless you want to enter a world of frustration :)