Taking off old rotors, they may be stuck in place, might have to use a Mallet and whack them from behind a few times to break them loose,due to rust.
Here is a tip for you, grind off all the rust on the hub and the back of your wheels before putting the new rotors on, use a wire wheel attachment, you can use it with your drill, just be careful not to scratch your wheels.
Also when you put the new rotor on, put on all your lug nuts and snug them, rotate the rotor, make sure everything is straight and the rotor turns without wobble, then install your brakes, then remove the lugs, install wheels, then put lugs back on.
Take your time, it can be a easy job, but better to take your time.
Grinding off rust is an option, but it will keep everything flush and straight.