I need a step by step for replacing sparks plugs on a 1992 Lexus LS400

I don't think I've ever worked on one of those... I can give you general instructions, though. First of all, you probably have some plastic covers on your engine - remove them first. Then remove your plug wires. NOTE: it is a good idea to mark them first; normally they are in specific lengths and will only fit back on one way but you do not want to mix these up! Find out what the pug gap is for your engine (most cars have the plug gap included in the info on the engine decal stuck to the underside of the hood or elsewhere in the engine compartment) and gap your plugs. If you cannot get them exact, a bit smaller is better than a bit bigger - gaps grow over the course of use from all the heat. Taking care NOT to get any dirt in your cylinders, (best blow with compressed air around the plugs first) pull your old ones using a spark plug socket (regular deep sockets lack the rubber boot that protects the ceramic). Have a look for any abnormal conditions when they come out: are they black? wet? white? all different? these conditions will tell you if there is something else going on in your engine. Check the box of new plugs for torque: usually the package will say something like 18 ft-lbs or quarter turn past snug or something like that. This is very important - tighten just a hair too much, you pull threads out of your head - tighten not enough and you risk having them be blown out. IF package doesn't say: is there a crush washer? If so, go finger-tight then 1/4 turn; if not, go finger-tight then 1/16th turn. If you can't get your fingers in there to turn the plugs in, use a piece of rubber hose stuck on the tip of the plug and spin the hose.