Start with the bicycle upright with the weight resting on the tires (wheels on the ground).
Loosen clamping bolts on Stargazer stem with a 4mm allen key.
Lift the rubber cap on the top of the stem. Under it is the headset compression bolt; it is in a vertical position. Remove this bolt completely using a 5mm allen key.
Pull the Stargazer stem off the steer tube of the bicycle. If the wheels are on the ground there will be no issues, but if the wheels are off the ground make sure the fork doesn't fall out of the frame.
Without removing any headset spacers, slide the stem riser onto the steer tube. It will look like the picture below. Leave the hardware loose for now.
Insert the compression bolt inside the steer tube and tighten the bolt until it's snug. See the picture below for where it installs. You want to make sure that there is no play in the headset bearings, but you also don't want to overtighten this bolt. The loosest setting that eliminates play is best. To test this, grab the headset spacers with two fingers and try to spin them; you should not be able to. When grabbing them with your hand you should be able to spin them.
You will not need the top cap that came with the stem riser (pictured below).
There will not be a compression bolt under the rubber cap of the stem since it's already inside the stem riser.
Install the stargazer stem on top of the stem riser. Once you have aligned the clamping hardware on the stem riser and also the stem to the front wheel you can tighten down all the clamping hardware (horizontal bolts). There are two bolts on the stem riser (use a 6mm allen key) and two bolts on the stargazer stem (use a 4mm allen key).