Visas are not extended. Only your 90 day permit to stay can be extended and you could apply for one near the end of your current 90 day entry.
What is the basis for your non-o visa.
If married to a Thai you can apply for 60 day extension to visit them or a one year extension of stay.
You can use your visa for entry and get a new 90 day entry by land, sea or air.