out the bottom bud, best way. put car on stands, remove bottom covers and protection plates, remove downpipe, oilfeed, oil drain, turbo inlet+outlet, turbo to manifold bolts .. (have to remove the airfilter for this..)
then with a lot of patience, manuver the turbo past the steering collum (or if you find it easier, remove the bottom part of the steering collum) and it will eventually drop out.. its a tight fit, and has to be turned just right, but it does come out like that, i have removed mine like this.
if im not mistaken, this is the procedure bmw describes in their TIS too.. dont be tempted to take it out the top, it will mean removal of the injectors, which is always a risk.. i will see if i can somehow copy the instructions directly from TIS, and post it here.
edit : looking at TIS, seems bmw wants you to take it out the front, by removing the egr, fan shroud and driver side intercooler pipe.. out the bottom is easier