Replacing old receptacle with GFCI receptacle. Old one has a single white wire attached top right next to the ground. And it has two black wires on the same screw on the bottom left. One I assume is the hot line because the other one goes into a switch to the overhead fluorescent. On the new GFCI do I move both black wires to the upper line side? Or do I only move the hotline to the top and connect the one to the switch through the bottom load? Thanks