I have an EAD based on my V-1 status; how is the renewal done? Where do I send it? Do I send it to a service center or do I go to district/local office? Do I mail the original or just a copy of it?

I was also wondering if one has to pay again the 120 $ fee? thank you

yep, you got to pay the fee. I think EAD renewals are done by mail (most of them). Check www.ins.gov for the office in your city because it might be different.