I'm doing weather strip right now and I have done B pillar in the past,. Its pretty cut-n-dried...remove any screws, TRY to peel up an end and slowly pull it up as you go, if it will stay intact. At some point it will probably tear and leave chunks in the track. Scrape those pieces out with a screwdriver or some other tool that will fit in there. The Track has to be absolutely free of old rubber in the bottom or inside grooves. The BEST tool for that is a dremmel tool stainless wire wheel. It fits perfectly insiden the track edges and cleans all the old stuff out. Finish with the standard wire brush.
To install the new, use a bondo spreader to push the edges into the track. Use one thats at least 4" wide. Get a small piece started then use the spreader to get on top of that and a couple inches of rubber thats out and push it in and just keep moving pressing 1 or 2" sections at a time. Use care not to cut or tear the rubber. Thats why I use the plastic spreader and not a metal tool. Do not let the rubber stretch or you will have leftovers at the far end. Some people install both ends and work toward the middle so this does not happen.
On all pieces, I will install once for a fitting, then pull it out and re-install with a very minimal amount of glue. Some pieces do not even get any glue if the fit was nice and they have no danger of being pulled out by the door or top.
Finish after checking the glass fit and sealing, by applying a coat of amour-all GEL to the exposed part of the rubber. Some guys use silicone grease. Just some form of thick silicone to keep the surface soft and protected. This also helps prevent anything from sticking to it and trying to pull the rubber out of the track.
If you have major rubber/glue issues with the old stuff stuck in the guide track, a 3" wire wheel on a drill will scrape it out then the dremmel tool can be used to clean down inside the edges. I used an old sheet to cover the car interior while all the rubber flakes and grit was flying around everywhere. The old 3-M adhesive tries to stick in there for the next 100 yrs. Its the rubber that comes apart. With the right tools and some luck, its not a bad job. My A pillar took 30 minutes. My 2 top side edge seals took all day.