If you have another manufacturers brake pad materials on your discs, then you definitely need to clean them up or get them turned by a professional before installing G-Loc™ brake pads.   To clean your discs, use a power sander with no less than 80 grit sand paper, and some brake clean to the disc surface.  This is to break up any of the other material on the disc surface.  DO NOT get any brake clean on the G-Loc brake pads.

If you have had ONLY G-Loc™ brake pads on your discs, then there is no need to resurface or turn them.