There is a easy way to update Grbl or other firmware on board.
In Engraver Master software. In order to get the latest firmware, please Update Engraver Master first.
Click the Menu button top right of Engraver Master.
Select the update firmware menu.
Select the firmware version, or load other firmware file with a .HEX extension name.
Click Update Now. You can find the led lamp flashing on the board. It will be finished in about half a minute.