Is there any way I can downgrade iOS 8.1 to ios 8.0.2?

I have a iPhone 5s 16gb

No downgrading isn't a easy thing to do especially on newer versions of ios
i'm afraid you are stuck on 8.1

There's a newer OS coming out soon that addresses many of our complaints with the previous upgrades - mainly, SLOW service on 4S and 5S phones. So wait - or go read on tech sites. I'm holding onto my 4S until either I go off contract (12/27) or the Black Friday sales convince ATT to let me do this early. Off contract, I can get a new 6 for $199, and sell my 4S for over $100 - the ATT phones sell for more, because of quad service. I could jump providers today, but since I travel internationally, I want the quad-band service - so ATT it is. THEY do not have to know that - but I can wait it out. I figured out that for every day I wait, I'm saving almost $8 - so no rush - and if the iOS update makes my service a little bit faster - closer to what is WAS - then I can wait. So see if the latest upgrade coming out fixes your complaints - that is what many of us are doing.