I wanted to know how to replace the fog lights on a 99 lexus es 300?

Do you want to replace a burned out bulb or a broken lens?

Bulb replacement is usually easy...reach up behind the lower air dam and turn the bulb base to disconect it. There may be a clip you have to depress to allow it to rotate.

If you cannot get your hand back there or it is too hard to do without seeing it, sometimes the lens is held in place by spring-loaded tabs and can be gently pried loose with a flat-blade screwdriver or small pry bar covered with electrical tape (to prevent scratching). If you don't see any exposed screw heads, then this is probably the case. Otherwise, remove the screws holding it in then gently pry it loose. Then you should be able to see the bulb base to remove it.

The same above goes for replacing the lens itself...good luck!