There's a couple of channels on YouTube that are specifically for DIY fixes on BMW's and X5's. Nathans garage is one that I can think of off the top of my head that has a lot of DIY "do it in the dirt" videos. Some of the videos are produced well, and others not so much...

Just type in "BMW E53 X5 rear upper control arm replacement and see what happens. It wont hurt to watch a few videos and take notes. I've never done this swap myself so I don't know the difficaulty of it. But I would say it wont be too hard.

Just make sure that you take your X to an alignment shop and tell them that you want the camber taken out or what ever you want.

Nathans Garage: https://www.youtube.com/watch?v=YSW_sst_irw

Autodoc: https://www.youtube.com/watch?v=3rZiU80PWuo

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Running:
2001 E53 3.0i Black 5MT Style 87, Eibach Swaybars, Headers, Turner Monoball Bushings, Oil pump nut fix, E60 short shifter + ZHP shift knob, Sport Swap 204K (G-power supercharger coming soon)
2011 E70 35d Blue Style 214 3" exhaust, Dudmd stage 2, 2" HR lowering springs
2012 E70 35d Black Style 215

Sold:
2002 e39 540i 6MT Black sport, M5 LSD, M60 Intake manifold
2003 e39 525i Auto Grey Sport