That’s going to depend on the office but generally you’ll probably need to fill out the form TM47, a copy of your passport photo page, a copy of your last entry stamp and a copy of your visa or extension stamp.
You can’t cancel a visa. You may be allowed to apply for another visa type that will supersede an existing one. For example if you have a DTV (for 5 years) you could apply for a Non B to allow you to work in Thailand for say 3 years and then go back to the DTV for the remainder.