Yeah, this is a really easy fob to change. CR2450 battery. Pull out the valet key (press the button near the top of the fob to release). Then insert a flathead or the valet key in the hole where the valet was, and use that hole to pop off the back off the key fob. It takes a little pressure, but will pop off pretty easily.
I made a quick video of changing my own:
Also, for guides to every other x3 fob see:
https://fobbattery.com/vehicles/bmw/x3/