Seems like lots of people are having issues woth these leaking, but there doesn't seem to be a good write-up on how it's done. I am about to tackle this on my 2015 320i. It doesn't look like it's possible to change the lines without removing the turbo, but I found a good video on YouTube I wanted to share with you guys, since I'm going to try this before removing the turbo.
This guy reasons that the leak is likely coming from the turbo side of one or both of those lines. Since they are situated so close to the exhaust manifold, it does seem reasonable that these gaskets would certainly deteriorate faster, causing a minor coolant leak. In my case I didn't notice any coolant leaks at all. A couple weeks ago, the head of the coolant bleeder screw in my expansion tank blew off on the highway, leaving me stranded. I had it towed home, drained the cooling system, installed a brand new expansion tank, aluminum coolant flange, and since I was right there anyway, did the upper radiator hose, and vent hose (to expansion tank).
When I pulled vacuum on the system to fill it, I could see that there was a small leak somewhere because the guage was dropping. I turned off my compressor to listen, and sure enough, I could hear a tiny pinhole leak sucking in air. I couldn't actually see it, but it was coming from the turbo. What I COULD see was some white residue on my exhaust manifold that I believe is from coolant. Anyway, I'm gonna try it, and here is the video. I'll take pics and report back to y'all after I get done.