How do you remove the rear tire on the D609G Troy built lawn tractor?

Hi,
That is an incomplete model number; it should start with 13 and a letter, end with one of the Troy-Bilt vendor numbers like 078. At any rate it is a 600 series frame, i.e. 609 and has a 42" deck, the G. If you mean wheel removal, it is either a bolt or an E-clip covered by a hubcap of sorts. If you speak of the tire from the rim, then you need to deflate it by removing the valve stem core, breaking the bead loose from the edge of the rim and pry one side of the tire over the rim while simultaneously pushing the opposite side downward so that it goes into the recess in the wheel that allows you to be able to pry the other side off.
Peace,
Clarke