These procedures will show you how to remove the factory muffler from your 993, the installation is the reverse of these steps. 

Basic tools needed to complete this job: 
2 x 13 mm open or close end wrench
Snap ring pliers
13 mm socket and 10 mm socket with ratchet
6 mm hex key (only needed if your car is 96 or up)

Step 1:  Loosen the 13 mm bolts that holds the exhaust tips on

Step 2: After removing the bolts, use the snap ring pliers to spread open the flange that secures the tips to the muffler and remove the muffler tips.

Step 3:  Loosen the 13 mm bolt that is on the flanges on the other end of the muffler pipe that attaches to the CAT.

Step 4:  Use the snap ring pliers to open up the flange and slide the flange so it rests on the CAT side.  This will save you a step when installing the replacement muffler.

Step 5:  Remove the strap that holds the muffler in place, on the 95 993s that strap is held together using a 13 mm bolt, on 96+ 993s the bolt is a 6mm hex bolt.   Slide the strap out of the way and lift the muffler up from its clip and the pipe that is resting on the CAT.  the muffler will drop down.

Step 6: This step only applies to RSR Special customers, I do not include the heat shields on the RSR Special when I send them.  You will need to remove the heat shield on your original muffler using a 10 mm socket to remove the 2 bolts and remove the bolt clip underneath it and transport it over to the replacement muffler.

Installation procedure is the reverse of these steps.  When mounting the exhaust tips back do not tighten the bolts all the way, leave enough slack so the tips are still moveable.  Once the desire position is adjusted tighten the bolts down. 

P.S.  The mystery muffler on these pictures is the Fabiani 2nd generation system.  Donor car for this DIY is my 96 993.