I was a lineman in the 8th grade and my coach said i should go for free safety in high school. What do i do?

He is gonna be my coach there to because the High school is new and he said hes opening it. He told me face to face he would hate to see me get hurt or possibly dead. Since I have good power he says to be a free safety but i don' t have the speed. I am a 5'11" 189lb football player. Please help me i don't know what to do since I'm so confused i keep thinking i should just give up on football all together.