1990 GMC Sierra fuel pump replacement

I am in the process of replacing the fuel pump in my truck. I have pulled off the bed to gain access to the top of the tank...a little easier than dropping the tank. Im stopped in my tracks...I can not get to the fuel pump. How do I remove the access ring to get into the tank, and to the pump? I have tried with a hammer and screw driver and channel locks to remove this??? Counter clockwise doesn't seem right. I've tried both ways with no luck.