Help with setting impediance level for Polk rti a7 speakers

Hi guys I have the Polk rti a7s 8ohm speakers and I will be setting them up to A DENON poa 2800 200 Watts per channel at 8ohms and 400 watts at 4 ohms. My speakers are rated at 20 - 300 watts output. My question is how do I set the impedance level of my speakers from 8ohms to 4 ohms ? Sorry I’m new guys so yeah all help and tips are welcomed.

Thanks

Tony