The assembly on the E46 is extremely easy to remove, there is one button/clip that you pull inwards and the assembly pops out. The assembly holds all like... 5 bulbs that are in your tail light, just find the brake one and twist it one way and it will pop out. Then just insert the new bulb, push down and twist, and its good to go.
Then you simply place the assembly back against the housing, line it up, and push it in and the button/clip will click and you are good to go.
Very easy install