Your car must be on a lift or up on jack stands to do this BMW E46 Manual Transmission Fluid Change. You should not do this fluid change with only one end of the car up in the air as you will have problems completely draining the old fluid and not over/under filling with new fluid. The car needs to be level to do this correctly.
This BMW E46 Manual Transmission Fluid Change contain 5 steps :
Step 1: Getting the required items together
Step 2: Getting Started Under the Car
Step 3: Locate the Transmission Fill and Drain Plugs
Step 4: Draining the Old Fluid
Step 5: Filling the Trasmission Fluid
Step 6: Replace the Plastic Shields

BMW E46 Manual Transmission Fluid Change Link