So "speed" here is a bit of misnomer this is looking at how much to step up for each z layer or changing the vertical resolution/quality. A 0.4mm nozzle (the norm) you can go to .2mm without layer adhesion issues coming up but will lose some quality, typically mk3 uses .15mm layer height for a good mix of quality and time to print. Actual motor speed can be changed in firmware if the control board used Marlin the open source software most controllers use, and has a USB port then can possibly change those values too (mm/s on given axis or adjusting acceleration for the axes) but that is more in depth akin to flashing betaflight on a FC (but using Arduino ide to do the flashing since they are mostly using compatible processors from Atmel), in that case would want to increase the temp probably as well if extruding faster. Long story short changing the slider just changes how high each layer is so does less layers for a given model if each layer is taller.