You will have to depart the country and apply for the 60 day SETV visa at a Thai consulate/Embassy…you can go anytime within the 45 day visa waiver stamp window but i would do it towards the end (last 3-5 days to maximize the 45 days)…you can go via land or by air, you can go alone or with a visa agency, totally up to you just make sure you fill out the paperwork and get an appointment at the Thai consulate/ embassy of your choice…once you return if you’re in Bangkok you can go the same day to the immigration office and ask for the 30 day extension as long as it’s still during its business hours…good luck
yes you can have the 45 day visa exemption stamp in your passport if you have a passport that allows that, then at immigration you pay ฿1,900 for the 30 day extension
You can get the 30 day extension the same day you land as long as the BKK immigration office is still open at that time…. So go whenever you want in the 45 days you probably have with your visa exemption stamp…beware of the dreaded lunch hour at the immigration office it will turn into an all day affair…