If I am from a visa exempt country my stamp is good for 30-45 days …. If I want to stay longer do I have to leave the country and re-enter for another 30 days or can I just extend my stay by going to immigration. I want to stay for 60 days
TLDR : Answer Summary
If you are from a visa exempt country and your stay in Thailand is valid for 30-45 days, you can extend your visa exempt stamp one time by visiting a local immigration office for an additional 30 days without having to leave the country. This means you can potentially stay for a total of up to 60 days.