Changing oxygen sensor & brake rotors

How hard is it to change the oxygen sensor in the front, do i have to have a special tool ? And how hard is it to change brake rotors ? I think i've heard something about you being able to filp the rotor to the other side and use them is this true ?

I don't think you can flip the rotors. That sounds like an old wive's tale to me. They are not hard to remove, but you must take off the brake caliper and mounting brackets. But, I am wondering, why do you think you need an O2 sensor? If you do, it takes a tool like a large socket with a slit in it to protect the wires. But you can use a large wrench if you have enough clearance. Let me know what symptoms you experience.

The symptoms that i am having is that my car is eating alot of gas, when i am on a hill going up the gas gauge goes down like i am losing gas and when i am on a hill going down the gas gauge moves up saying that i have more gas that i do. Any idea what this can be ?