the car has 94000 miles, and l bought the car used, it had all its maintenace from LExus dealers, but l think they use normal toyota conventional oil5W30, l am thinking of switching to MOBIL 1 FULL SyNTEC, should i, or is it to late, or should l just stick to convetional?

You can switch just keep an eye on your oil. Synthetic due to it is lubricity will sometimes get by the rings in higher mileage vehicles so as to be using oil. If you change and notice that the vehicle is using oil then try going to semi-synthetic or back to regular oil.

You should use Lexus recommended Synthetic Blend by Quaker state. It last 5,000 miles and it is not as expensive as full synthetic.