Find the firmware here:
I would recommend using 1.9. That’s the most stable. I use 1.10.0. Has an error that prints freeze at 99% on occasion even though they’re done. (can be fixed editing g-code comments at end) Doesn’t really bother me since I do a lot more laser and cnc.
Put it on a usb drive (recommend using the one that came with SM) and insert into SM.
On the control pad swipe left and under settings you’ll find update firmware.
Select file and start it. (Occasionally it will freeze. Give it 10-20 minutes and then turn power on and off and try again)
-S