I have replaced an upper control arm about 5 years ago and as I recall it really isn't too bad. I did this because the ball joint was bad. Made a significant difference.
You have watch the spring- I held the car up with jack stands and then support the lower control arm with the floor jack in order to manager the spring. The arm comes off rather easily.
Check the big rubber bushings, especially the ones for the sway bar, they often need to be replaced.
The inner bolt is a bit tight but not too bad. Remember the bolt/nut orientation, makes reassembly easier.
Releasing the outboard end with the ball joint just required some banging to get it to release. It is a tapered fit, BTW so once you get it to move, it comes right out of the wheel hub. I used some heat I believe. Watch the brake line on the caliper, once the ball joint is free the hub will want to fall outward.
I still have the old arm, it sits on my desk. Since it is all aluminum, I used a steel brush on a grinder and buffed it out. People ask me all the time what it is. Some I tell them it is a landing gear strut from the Moon Lander ..... they buy it until they look closely and see the MBZ star on it ....
Hope this helps,
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)