How to update firmware (MK4/S, MK3.9/S, MK3.5/S, XL)

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On printers with the xLCD with a USB drive connector, the firmware is flashed using a USB flash drive.

1. Download the latest firmware for your printer and extract it (zip file) on your computer
   • Original Prusa MK4S
   • Original Prusa MK4
   • Original Prusa MK3.9S
   • Original Prusa MK3.9
   • Original Prusa MK3.5S
   • Original Prusa MK3.5
   • Original Prusa XL
2. Make sure the USB flash drive doesn't contain any previous firmware (.bbf file)
3. Copy the new .bbf file to the root directory of a USB flash drive (Not within a folder).
4. Insert the USB flash drive and push the reset button. The bootloader will automatically compare the installed version with the one on the drive and, if newer, will automatically offer you to flash it.
5. Confirm the update by selecting the "FLASH" button and pressing the knob. 

If you need to downgrade the firmware or re-flash the same firmware, follow this guide: How to downgrade firmware.

Factory Reset

If you do a hard Factory Reset, the firmware that is in the USB will also be installed in the printer, so this can be used as a way to update the firmware.