Actually they are pretty easy to change out.
Remove the fender. Trust me it is much faster.
On the old roller just drill out the bottom. Just be careful to use the right bit.
The trick in getting in the new roller with the door sprint is this.
Make sure door is close. Grab a piece of 2X4 about 4 foot long. Carefully place the end against the edge of the 2x4 so that the bar is against the spring . Place a towel or something between the 2X4 and the cowl. Use the 2X4 to push the spring back so that the roller can slide down. Just be very careful NOT to put your fingers in such a way if anything slips you wont get hurt.
Personally I used a tool that has flexible fingers on the end of it.
Also check out
http://www.oreillyauto.com/EW3/HomePage.do auto part # 2168PK. They had a kit in the HELP section at the store I was in just the other day.
It took me about 20 min to do mine.