I prefer doing the reset in the menu under Settings before I go to any tricks like power and volume buttons. That usually clears up the sluggishness.

As to Android I will share how I find out but first I rarely suggest this if speed is to be maintained. The newer OS should be bigger and the port is rarely optimized so if you feel speed is king then stick with stock,

OK, here's my google words. "Lenovo Tablet A5500H xda forums"

The first hit is https://forum.xda-developers.com/android/general/lenovo-a8-5500-hv-a8-5500-h-roms-t2836866 but I didn't find a version past Lollipop. You would have to read through to see if anyone did Android 6 or 7.