For your particular device the switch is integated into the device so you don't get to choose.
Power in must always equal power out. Watts STAYS THE SAME (in reality it actually decreases due to losses). The circuit does NOT add watts. It does NOT output more energy than you put into it- that is a perpetual motion machine. This means you can change higher voltage with lower current into a lower voltage with higher current, or lower voltage with higher current into higher voltage with lower current.
Now...the lightbulb is a fixed load. Which means if you increase the voltage going into it, it will also consume more current and get brighter. THis is because you are putting more watts into the light bulb. BUt to put more watts into the lightbulb you have to put more watts into the converter as well.
It's like a lever where you have force and distance/speed, and you can trade off force for more distance/speed or distance/speed for more force. Except instead of force and distance/speed, you have current and voltage.