Do I need to update the TM30 when switching from an ED visa to a tourist visa in Thailand?

The question on whether you need to go to the immigration office and cancel your stamp before you leave or not comes down to whether you're on the first 90 days of the ED visa OR if you're on an extension of stay.

If you're on the original 90 days you got from the ED visa you do not need to do anything and when you stamp out of the country you're fine

IF you're on an extension of stay you got from the immigration office you technically need to take paperwork from your school to the immigration office and cancel your extension

Don’t forget to cancel your extension (based on ED) before you leave Thailand, as it’s not cancelled automatically on departure, and you could face a fine up to 20,000 Baht for overstay on your next stay in Thailand.

Even though you may return on a new Visa, when you next report to immigration to extend/90 day report etc...they may notice that your previous extension of stay was not cancelled, and subsequently fine you for overstaying that extension!

If you are indeed in Chiang Mai like your profile says YEP, you will need to take your TM.30 receipt to the immigration office and let them update their database and stamp it when you come back into the country