You can increase the headspeed by increasing your throttle curve points, below is a 5 point throttle curve;

Point 1 should be 0 - that is low stick
Point 2 should be around 40-60 (half-way between bottom stick and mid-stick (1/4 stick), your preference)
Point 3 should be around 65-75 (mid stick, your preference)
Point 4 should be around 80-90 (half-way between mid-stick and full-stick (3/4 stick), your preference)
Point 5 should be around 95-100 (full-stick)

Here is a visual from Notepad (attached below) (can you visualize the curve now?)

You can reduce or increase any of these points in your curve to your liking, increasing them increases motor speed which increases head speed.

If you have a 3 point curve, something like this;

Point 1 = 0
Point 2 = 70'ish
Point 3 = 95'ish