[lkchris]

It's fun to use the special gauge to determine rotor thickness, and I have one, too, but it's not really a required tool.

Your rotors are allowed to lose no more than 2 mm thickness from new.

It's pretty easy to feel for a lip at the outside edge of your rotor, and if there is one it really can't be more than 1 mm higher than the rest of the rotor surface. Remember the same lip almost certainly exists on the other side of the rotor which is of course harder to see. So, 2 mm loss is 1 mm on each side. One millimeter isn't very much, and if you have any lip at all it's likely pretty close to 1 mm and it's time for new rotors. You've got a ruler or tape measure somewhere to remind you what 1 mm looks like.

And, it is senseless to put new pads on worn rotors.

And, to replace the rotors, you have to remove the calipers first and reuse of the screws that mount the calipers is forbidden.

All that being said, I'd have to add that for someone that's not sure where their brake pads are and (I assume) not really sure whether you even have wear sensors installed, I'd advise at the minimum finding a friend that's done it before to assist. Perhaps there's a VERY basic u-tube out there that would help quite a bit, but at your novice level it's pretty doubtful that a bunch a typed words from a forum will get you through it. In any event, attempting this and about any level of DIY maintenance without reference to a repair manual is not wise, to say the least.

Full disclosure: I used to produce repair manuals as a job. Mine was of course a Military situation and you were required to have someone read the steps EVERY time.