The supply line is 3/8" and the return line is 5/16". There are many different ways to replace them.
I replaced and re-routed my return line 3 years ago with some hose, 4 clamps, and basic tools in @ 30 minutes and she's still going strong. I took the return line loose at the pump (where the overflow valve is) and broke it off at the bracket by pushing it back and forth, then cut it off sqare and cleaned it up. Then I flipped it over and slid the new hose on and put two clamps on it. Then got under the truck and reached up as far as I could and cut the rubber line. Then I disconnected the steel line at the fitting, cut the steel line close to where the original rubber hose is connected, cleaned off the burrs, slid the new hose on and double clamped that end. Then reconnect the steel lines and drive on.
I've also had the fuel filter drain valve/water sensor give up on me, so you may want to check it out.
Good luck,
Scott