@Mark **********
you can never renew any visa :/ You would either go to a thai consulate and buy a new one, or you would go to the immigration office and apply for a yearly extension of stay by meeting the financial requirements of
-400K baht in a thai bank account in your name for 2 months before you apply for the extension
-a notarized letter from your consulate stating you get 40K baht a month in income
-three months of pay stubs and tax receipts and documentation from the company you work for showing you have at least a 40K baht a month salary