I only have 2 wires coming out of my ceiling electrical box. Both are green, though there was a fan attached to it previously so I know one is hot and one is the ground. The Harbor breeze fan I just bought has 4 wires. Blue for the light, Black for the Fan, White which is says it common to both, and a green ground. Would I need to replace the box in the ceiling for this? Or is it possible to do it with just the 2 wires currently there?

I figured it out finally with a little more trial and error =)

Glad you figured it out because we would never know what to say with 2 green wires. Whoever wired the box back in the day needs to go back to electric school. Colors mean things with wiring, green is ground, not hot, not neutral, jsy ground. No current can be on green.