Slow-close toilet seats, also called soft-close toilet seats, work through means of hydraulic hinges located at the back of the bowl. These hinges help prop the toilet seat open when it is in the raised position and provide friction when the toilet seat closes so it doesn't slam shut.
Close the slow close toilet seat if it is not already closed.
Position yourself on the floor underneath the toilet seat so you can see the bolts sticking through the back of the bowl.
Unscrew the nuts threaded onto the bottom of the seat bolts. Use a pair of pliers, if needed. If the screws and bolts are rusted together, use a hacksaw to saw between the bolts and the toilet bowl. Remove the toilet seat.
Clean off the area at the back of the bowl with a rag and disinfectant. Use a wire brush to remove stubborn mold, mildew or stains.
Slip new bolts into the underside track of the new slow close toilet seat. Bolts should come with the new seat. Place the seat on the bowl so that the bolts go through the holes in the rear of the bowl. Open and close the seat to make sure it opens smoothly. If there isn't enough room for the seat to fully open, flip the bolts in the tracks. Replace the toilet seat in the bowl.
Align the soft-close toilet seat so that it fits across the bowl evenly. Screw the bolts onto the lid nuts on the underside of the tank. Secure them snugly, but don't overexert pressure on them with a tool, as you can crack the bowl's porcelain.