Removing a couple of courses of tile work to replace a damaged shower pan will be destructive and create a lot of work. If your shower unit is old, there's a chance you won't be able to find replacement tiles should any break. Fortunately, you can remove your shower pan without causing any damage to your tiles at all, even if the pan is closed and secured to your floor.
Remove the front panel from the shower pan. If the pan is secured directly to the subfloor, use a handsaw to cut away a section of its front to expose the drainage system.
Shine a flashlight into the cavity beneath the pan if there is little natural light.
Unscrew the trap connected to the drain hole in the pan. Use a pair of pliers if the connectors are stubborn.
Cut the silicone sealant around the perimeter of the shower pan with a utility knife. Make an incision where the sealant meets the tiles and where it meets the pan. Be careful not to scratch the tiles while you work. Then cut the sealant into small sections and use the tip of the utility knife to pull it up.
Knock the top of the pan with a rubber mallet to displace any residual sealant.
Ease the shower pan out from beneath the tiles by gently pulling it toward you. Intermittently apply pressure to opposite sides of the pan if it is hard to move.