First of all, you have an inline-6, not a V6. You do not need to remove the radiator, or even the fan. I am in a litlle bit of a hurry right now, but I think you can find what you need here: Pelican Technical Article: BMW Belt Replacement
I haven't read de DIY, so I am not sure if they mention this: removing the airbox (where the air filter is housed) will greatly ease access to the belt tensioner.
Good luck, and don't believe anyone who says ou need to remove the radiator or the fan. It is really a much easier job than that.
Good luck, and welcome to werkz.