is there a special tool that ii would need to buy to replace the o2 sensor before the catylitic convertor or is it pretty easy? if there is a tool that i need to buy where can i find it? thanks

They make a slotted socket that makes it easy, but if it's really stuck, you'll have to clip the wires and use a spark plug socket to remove the old one, then use a wrench to re-install it.

thankyou very much for your help