@David **********
, You just leave and enter Thailand again (simple border bounce using your multiple entry visa) on or a few days before 4th October, you will be stamped until around the end of this year.
After that, you can do border-bounce to enter on visa-exempt for 30 days.
Or go for visa-run to apply for a new visa (Single Entry Tourist Visa) and enter Thailand on it being stamped for 60 days.
Both are eligible for 30 days tourism extension at the local immigration office (not an embassy).