on my 02 lexus es300 tires.? what tires are more important to replace, the front tires or the back 2 tires?because l only have 2 brand new tires?

The better tires should always go on the rear. For reasons why check out the links below. If you do not have time check out the Michelin video (last link) at the very least.

the old way of thinking was that always put new on the tires that r 'driving' so that for if it is front wheel drive like the ES is, then front new. If RWD (like say the LS) then rear wheels. It is been shown through the years now, that it is more important that the rear (no matter what drive) should maintain traction over driving because it is always harder to correct ur vehicle when ur rear end goes out & slides, than if ur front turning wheels go. Just think of situation in snow, if ur rear end starts sliding, they r fixed forward & will just continue to slide in the direction it was heading. Your front tires, u r able to steer no matter what, so it gives u a chance to 'direct' the slide.

You may now think ''well, if front r directing, l want more traction there right?'' no, because the main idea is to ensure ur rear does not slide out in the first place.