@Yoana *****************
You are not renewing it. You are getting a current dated one showing you are still legally married. You can go to any district or sub-district office in the country to get it. You do not need to go to the office that registered your marriage. It is a nationwide online system. Tell them you need a Kor Ror 2. They will print it out and sign it. The cost is 20 baht. You should not need an appointment. Just go to the office, get a queue (if they have them) and ask for the form. Once it is your turn it should only take a few minutes.