not sure about the tire question but changing the upper control arm is a matter of supporting the vehicle, separating the upper ball joint and then unbolting the frame attachment. the lower control arm compresses the spring against the frame spring support and the shock should limit the sudden decompression of the spring when you separate the ball joint.
The pain in the butt part is removing the old ball joint from the upper control arm. It is actually threaded in and you need a special socket for an impact wrench to get it out. Having said that, I've done 4 upper control arms already and stripped every one. of course, the control arms are 45 years old in my case. The new balljoint threaded in but with less than confidence inspiring feel. I ended up tack welding the upper arm to the ball joint for peace of mind.