A: This step is not designed to support additional risers outside of the ones included.
A: The maximum height with both risers is 6"
A: It says 300 lbs on the website
A: I asked and heard back that you cannot. I would not recommend this if you're trying to go above the height here.
A: This step has a non-slip surface so it can be used on carpet or hard flooring.
A: Highest level: 6 inches, Lowest level: 4 inches.