I recommend wearing a hockey cup to protect the groin. With gear shift in 2nd or 4th, position yourself on the center console, left foot planted on floor of driver side and right foot passenger side for leverage. Be careful, this is dangerous. Pull knob toward you using both hands. Knob will pop off when the amount of pulling force is sufficient and when that happens, the top of the knob will inevitably hit your crotch like a missile, then the rest of your body will propel itself into the backseat. You are now ready to install the new shift knob. Good luck and welcome to Bimmerfest.
Dave