How do you change spark plugs on a 1999 Lexus GS 300

Same way as the lawn mower.
Unscrew the old ones and screw in the new ones

Lots of luck

^ ^ ^ ^ ^ ^ ^ ^ ^ wat e said !

un-bolt the coil pack, take the plug out put the new plug in, replace the coil pack . repeat 5 times
.job Done.

Lefty-loosie, righty-tighty.

Easier said than done. No one told you that you have to split the intake manifold, remove the coolant lines, and hope and pray you do not get coolant in the intake valley or you will have a misfire from the coolant pooling inbetween the spark plugs. If in doubt take it to a professional. You probably wouldnt want to mess up your car.

sirquest2001 is right on the money. its a real pain in the a$$ to do on the 2jzge.. to replace the front 2 spark plugs is a piece of cake.. but to get to the last 4 u do need to take apart the throttle body & intake manifold. while you're at it replace the valve cover gaskets aswell because u might aswell as they r guaranteed to leak after some time. dont trust some sleazy mechanic either because those guys will only change the front 2 spark plugs because they dont wanna fuss with the whole thing.