Can I switch from a 6 Month ED Visa to a Tourist Visa without leaving Thailand?

There is no such thing as a 6 month ED visa. :/ Did you get a 90 day ED visa and then extend it for 3 months at the immigration office for 1900baht using documentation from your school?

IF you did you would have to go to the immigration office and cancel the ED extension you're on before you leave the country to go get a tourist visa from a thai consulate

And no you can't get a tourist visa for thailand inside of thailand, you get them at a thai consulate in another country.

you have to leave the country to get the 30 day Visa Exempt, apply for the 60-day SETV or 6-month METV...the only tourist visa you don't need to leave country for is the Thai Elite Visa...