If you have an above-ground pool, there will come a time where it will be inevitable to change the liner. After years, the liner may become cracked from chemicals and the sun or something sharp may have cut the liner beyond repair.
Replace Overlap Above Ground Pool Liner
Empty the pool if it is not already empty. Place the submersible pump in the lowest part of the pool, usually the center. Make sure the drain hose is away from the pool and the water is not coming back towards the pool. Usually this will drain all but an inch or two from the very bottom. Get into the pool and you can push the sand down and get out some more water with the pump. The last little bit of water will be taken out by sucking it up with your wet/dry vac. Hand it out to someone else when it's full and repeat until all the water is gone. It goes faster if someone gets in the pool with you and uses the broom to push the water towards the vacuum. Have the other person get out and take out the ladder.
Disconnect the skimmer and inlet from the pump and remove it from pool. Remove the liner by cutting it into smaller pieces with a utility knife. Be careful not to let the knife touch the walls of the pool, as it will scratch and leave sharp pieces that can damage your new liner. While you are doing this, another person can be taking off the caps and top edge (rails) of the pool. Start at a certain place and mark the rails 1 through how many there are so you make sure they go back in the same place they came from. Put the screws from the caps and rails in separate jars or coffee cans and label where they came from. You should be able to get all but the top edge of the old liner out while this is being done.
Once you have the liner out, inspect the inside of the pool walls. If there is anything sharp or any rust, sand it down. You can use a fast drying metal type spray paint to strengthen it if it's bad. Remove any old duct tape on the seams that's starting to come off and replace it with new. Take off the plastic or rubber clips that hold on the liner and remove the last bit of liner. Be careful not to crack the clips.
Remove any roots or stones have found their way to the top of the old sand. Check to see if there has been any critter activity that may have eroded or shifted the sand. If you need to, add your new bag of sand and use the push broom to smooth it out. Build up the sand around the outer edge to make sure the new liner will not get pushed under the walls. Smooth out the sand working from the inside out trying not to leave foot prints. You can make the bottom level or slightly deeper going towards the center, whatever your preference. Level is much easier to vacuum out.
Bring in the new liner and set it in the center of the pool. Carefully start unfolding it and taking it to the walls. Get the bottom centered and as flat as you can before you start up the walls. The easiest way to get the wrinkles out of the bottom is to use clothes pins to hold up the sides and use your push broom on the bottom to smooth it out. Start filling the pool. As the water is filling, keep smoothing out the bottom. The water will show you where the wrinkles are. You will only be able to move the liner around while there is less than an inch and a half of water. As the pool is filling, go around and let the walls down a little with the clothes pins. Keep doing this until the water is right below the skimmer hole and you will not get wrinkles in the walls. Line up your skimmer by putting a hole through the liner into the skimmer screw hole. Put a bead of silicone on the skimmer gasket. While someone on the outside holds the skimmer in place, push the gasket against the liner and screw into the outside piece of the skimmer. Hand tighten screws carefully as to not crack the skimmer. Cut the liner on the inside of the opening with a utility knife. Place a piece of wood or heavy cardboard on the inside of the liner where the inlet hole is. Have the person on the outside carefully cut the hole for the inlet hose. Put a small bead of silicone on the gaskets on the inside and the outside and hand tighten the screws. Now you can put the ladder back into the pool and get out.
Replace the plastic or rubber clips along the top edge holding the liner in place. Use a rubber mallet if they won't go on easily. You can also finish filling the pool. Put the rails and the caps on, and you have just replaced your pool liner and saved yourself some money. This project isn't hard just takes some time and patience.