How can I increase the torque or speed of the stepper motor with Arduino
To increase torque of 28BYJ-48 you have to perform a simple mod (cup one path on the PCB) to change it from unipolar to bipolar and then use it with an H-bridge like the A4988 or the DRV8825 driver.

Sources:

https://ardufocus.com/howto/28byj-48-bipolar-hw-mod/
https://coeleveld.com/wp-content/uploads/2016/10/Modifying-a-28BYJ-48-step-motor-from-unipolar-to-bipolar.pdf
https://everythingsmarthome.co.uk/howto/converting-the-28byj-48-stepper-motor-for-more-torque/
http://www.jangeox.be/2013/10/change-unipolar-28byj-48-to-bipolar.html
https://www.youtube.com/watch?v=hkxnQIKybiI
https://www.youtube.com/watch?v=jHLyJbNgcDo