How to increase weight when benching?

im 15 in my freshman year of high school. Im 6'2" and about 160-170. Im mostly muscular and i have some chub but thats not the issue. When people see me, theyre like "drew looks as if he can bench a thousand pounds!!" The problem is i can bench like 140 and thats it. I workout about 2-3 times a week. I have been lifting free weights for about 6 months and cannot increase the weights on the bar. How can i significantly increase the amount i can bench?