I suggest you download GRBL from GRBL github. you will probably want to decide if you want dual homing or pwm spindle/laser.
v1.1h has dual homing but at the expense of disabling PWM for a spindle or laser on clone Arduino boards -
v1.1f has pwm for a laser or spindle but no dual homing.
These are pre-compiled .hex files for loading with XLoader. Info here.