Just head on down to the local auto-racing shop that sells Earl's brake line kits and follow the instructions. Before you go out and spend a lot of money, I'd start first by making sure that the stock brakes are up to spec and that you have fresh Dot 4 or 5 brake fluid, depending on what the manufacturer specifies, preferably a high-temperature variety such as Motul. Rebuild the master cylinder and caliper if they need it. Then make sure the rotor is straight. This last item is probably the most frequent cause of poor brake performance.
Some systems bleed easily, some are nearly impossible to get completely bled.
Then, squeeze the brake lever while lightly tapping the banjo bolt with a wrench. If your brakes still fade, try experimenting with pad compounds. I don't know off hand what will work on GS500s, ask the people you race against. I'm still using the old asbestos Ferodo pads which are unavailable now, I have some Kevlar Braking pads to try on the RZ when the Ferodos wear out. Watch out for brake rotor temperatures with some modern Kevlar pads.