Where I work in San Francisco ,the average home is about 50-70 years old. During that time ,a shower pan will give out.I am one of the top shower pan mechanics in the Bay Area that gives an exclusive 10 year guarentee. So I will tell you step for step how its done. 

TOOLS NEEDED: Hammer , 8 lb.sledgehammer, rotary hammer, angle grinder, crowbar/flatbar

Step#1. Where protective gear,(eye goggles,dust mask or respirator,ear plugs and gloves.

       #2.  Have demolition tools in  hand.

       #3. One of the most crucial tools to use is a Angle Grinder( use Makita ,Dewalt, Bosch).The grinder is used when you go up  8-12 inches.from the base of shower pan.Then make your first cut going 1/8 -1/4 inch below grout joint and slowly cut around the perimeter of shower letting the tool do its work.DONT FORCE TOOL! as it will kick back and may cause injury.What I normally do is with the other hand ,I use a disposable water bottle with a hole on bottom spewing a stream  of water onto the blade as you go along.This keeps dust to a minimum(works like a champ!).Refill bottle using a 5 gallon bucket.Be sure that you have a sponge over the drain).Also cut into the curb preserving the tile trim outside or facade of shower using the same method(1/8-1/4 inch cuts from the grout joint.

       #4. The other tool that is essential to demolition is a rotary/chipping hammer.You can always rent one for the day.The next thing is to use your 8lb hammer and give the pan several good whacks to fracture the tile/mortarbed.Then,use your chipping hammer using a 1"spade and  take out pieces no bigger than 12 inches.You should reach the existing membrane. Remove all concrete debris.

      #5 .Now with a hammer and 5in 1 tool, chisel out the 1/8 to 1/4 in from the grout joints on the wall..the tile will come out easily.Then start hammering the walls on a located stud,use flatbar or crowbar to pry the cement tile wall loose..If there is chicken wire, use tin snipsbut LEAVE some wire so you can mesh with new wire...Now you should be down to the studs and subfloor of the pan.

      #6.Next have your plumber change the drain and drain pipe before doing anything else.

      #7. Have  the lower portion of walls supported with a length (8feet long) of 2x10 lumber,measure inside studs and cut snuggly to fit throughout perimeter of shower.This is to give support to membrane and mortar.

      #8.Next is to have your subfloor pitched properly before installing membrane. I use a product called pro-slope by Noble Company. Ive been using this for 5 years and you save alot of time .

      #9.Then with your drain,unscrew the 3 bolts ,remove upper part of drain,the apply a bead of NOBLESEAL to bottom part of drain clamp(Search for NOBLESEAL and NOBLEWELD for details on product installation).Use a 1-1/2 or 2" drain plug

      #10. Now with pan liner set, it is mandatory to water test your pan for 24 hours for leaks.If pan fails,inpsect all corners and and make sure all seams are caulked with Nobleseal, otherwise drain the pan .IMPORTANT:Make sure that your weep holes in drain are clear of caulking material.When you are draining the pan,three streams of water should go into drain in plain view.(This is what Plumbing Inspectors want to see.).The rest is mortared and tiled.