What steps do I need to take to extend my 60-day e-visa by 30 days in Thailand?

> I want to extend for 30 days when do I have to renew it

Chiang Mai, Bangkok, Buriram, Chiang Rai and a couple of others all allow people to apply for extensions when they have 45 days or less left on their current stamp. The other immigration offices are 30 days. However, ask your local immigration office for specific details.

>do I have to change my flight first

To get a 30 day extension of stay based on tourism, you will need to submit the following documents:

1. Your passport and:

a. a copy of your data ("picture") page

b. a copy of your most recent visa OR an e-mail print out of an e-visa (if you have one)

c. a copy of your most recent stamp

d. a copy of your departure card

2. A TM30, filed in the immigration office.

3. The forms (each immigration office may have different forms, and want to use their special forms)

4. 2x passport pictures (some, like Bangkok, may only require one picture)

5. 1,900 THB processing fee

>what will be the best visa to apply for

You will be getting a 30 day extension of stay based on tourism. If you have other reasons to stay in Thailand, then apply for the appropriate visa/ extension of stay.