As far as I know, you need change E_STEPS_PER_MM in motherboard firmware (file configuration.h):
0.706 if use 5mm splined shaft with no gearbox
2,2 for Adrian Geared extruder with standard stepping motor
2,02 for Wades Geared extruder with standard stepping motor
In new firmware I see 2 parameters (probably, for 2 extruders):
#define E0_STEPS_PER_MM 2.2 // NEMA 17 59/11 geared extruder 8mm diameter drive
#define E1_STEPS_PER_MM 2.2 // NEMA 17 59/11 geared extruder 8mm diameter drive
If you use not standard stepping motor, see: [
www.reprap.org]