Although my dick hasn't grown that much in sheer size... I think my head is pretty big in comparison to the rest of my penis.
One of the contributors may have been an exercise I do...
Get 90% erect. More or less... whatever is comfortable for you.. but definitely on the higher end of "semi-erect" and lube up, as if you were doing wet jelqs. Take your usual "ok" grip and grip tight at the base. Slowly, work your way up the penis... and whenever your head looks/feels engorged with blood.. HOLD it there for maybe 15 seconds..
Do about 10, along with your usual girth workout and your head should get bigger. Good luck! chicks dig a big mushroom leading the way for the rest of you cock.