Instruction to downgrade the current Android version of Galaxy A5 (2017) ???

Hi, I’ve been using the 8.0 Oreo Android version of A5. Just wanna downgrade this version to 7.0 Nougat because I miss the old theme and icons as well as interacting methods with the screen but dunno how to do it ??? Is it possible to downgrade an Android version on smartphone n does it cause any harm to my device ??? Any advice here ???