The return jet (eyeball jets) inserts that are originally installed in your pool are made so that you first unscrew the outer collar. You can then remove the outer collar and the eyeball; what you are left with is a threaded collar. The threaded collar should be unscrewed by hand. If the threaded collar proves hard to remove, you can use the KYP Tool (Aluminum Removal Tool). The KYP Tool will slide into the grooves, and you can then use a wrench or pliers from your toolbox to turn the tool and unscrew the threaded insert. Once removed, you will be able to install the KYP Pool Cooler.
Kool Your Pool installation instructions.
See section: "Removal of water return eyeball jet" for how to use this tool.