What is a patch?
A patch is nothing more than a file which fixes something that the original software neglected to do in the first place. Think of it as a fixit file for things that should have worked in the first place.
You can't uninstall a patch directly, but what you can do is re-install an older version of a patch in order to cancel out the newest patch. I'm assuming you recently installed a patch and don't like the components and are looking to uninstall. Therefore just reinstall the patch that you were last comfortable playing with. Hope this helped!
The patch will hold better if you remove the existing patch. If you patch over the existing patch, make sure all the edges are sealed off. If you are tired of replacing your vinyl liners, you might want to check out fiberglass as an option. A new fiberglass surface can be applied to your pool, and you will get a much longer life out of it. You can read more at: http://www.advancedpoolcoatings.com
First, glue the patch onto the area where you want it. That way, it will stay in place when you sew it. Bring the needle up outside the edge of the patch, and push it in to the patch near the edge. If you continue to bring the needle up in the fabric next to the edge of the patch, and push it down inside the patch, it will be much easier to apply.