Didn't notice you asked about removing it (was in a piss poor mood).
All you need to do is remove the four bolts on the riser and loosen the clamps. She should pop right out of there. You may need to squirt a little Dawn dish soap and water in between the hose and the pipes using a smooth screwdriver to break it free.
The gaskets for the riser should really be replaced annually anyway, they can be picked up from Sierra for cheap. Part number 18-0897 and Mercruiser part number 27-863724 (I think)...
Use Never Seize when you put it back together.
GT