Measure bed height from previous truck. Adjust hitch up or down to attain level of previous setup. If your new truck sits two inches higher than previous truck, lower hitch two inches. If you cannot get enough adjustment out of your hitch, you may have to raise or lower your pin box.
Keep in mind, any adjustments you do, will effect the clearance between bottom of 5er and truck bed rails. Your ideal clearance is around 6" plus or minus according to your setup and whether or not you travel always on pavement or off road. The more clearance you have gives the fiver more room to move when towing over uneven terrain, driveways, fuel stations, construction zones.
Others will chime in here and give you more valuable information. Good luck and enjoy your new truck.
Lakeside