how to loosen the faucet's tap flange?
As Tyson suggested, you should start by removing the screw cover


Use a small screw driver to pop off the screw cover (with the Moen
logo).
Next unscrew the reviled screw and attempt to pull off the handle.
If the handle doesn't come off, go to the hardware store and
    purchase a "Faucet Handle/Compression Sleeve Puller"





You should now be able to remove your flange