Try unzipping them into the same directory where you are downloading to -then open the unzipped directory. You will find directory "My Content" there. Open that one and you will see "presets". Drag that directory over to the DAZ Studio "My Content" and letting it go. It should ask you if you want to copy the new Presets to the other presets - say yes.

   After it copies, be sure to go in to the content manager and have it "scan known directories" to accept the new files.