Well, since he posted in the Audio section, I'm going to assume that HU means Head Unit, or the stereo itself.
The trim plate (that plastic peice around the radio) actually stretches all the way across the dash, around the A/C vents. To remove it, I usually start below the radio and just pull steadily--the clips will pop out, and you can work your way across the dash--tilt the steering wheel all the way down to make it easier. Once you have the trim plate off, there are just a few screws holding the radio in, and that'* it.
Just take it carefully with the trim peice, so you don't break it--but don't be afraid to pull hard enough to get the clips loose