I recently purchased an older home and wanted to install GFCI outlets in the kitchen. When I opened up the outlet, there were four wires (two black and two white) in addition to the ground. I watched a few videos ****** about installing GFCI outlets, but they only gave guidance about doing it when there's one black, one white and the ground. Currently, the two-prong outlets have all four wires attached - the two black wrapped around screws on one side and the two white wrapped around screws on the other side. What do I do with these "extra" black and white wires on the GFCI outlets? Attach them somehow or tie them off? Also, the ground wire is attached to a screw in the rear of the outlet box. Is that "alright"? That is, can I leave it like that and the new GFCI outlet will be grounded. Thanks in advance.