With *most* cars, the door panel it held on with plastic 'pins' that clip
into holes in the door itself.  You can get a special tool to help remove
these, but care with either your hands or a long screwdriver will suffice.  
The way I find out where the pins are is by touch.  Try to hok your fingers
under either the bottom edge of the door card, or on of the vertical edges.
If you can do that, and slide your had along, you should feel the first of
several pins.  Get as close to it as you can, and pull *gently* straight
out frm the door.  The pins do become brittle with time, you want to avoid
breaking as many of them as possible.  Once the first is out, things get
easier.

You may also find that the card sits in a channel top and / or bottom.  On
the nord cars, this is simple removed byt loosing all the pins, then
shifting the entire card upwards to free the channel from the door.  On the
Sprint, the card neds to be bent in the middle to give enough play to come
out of the channels top and bottom.

HTH.  I can't be more specific as I've never done a 155.