How do you remove the blades on a lawn chief 42 riding lawn mower?

Use a 9/16" Socket on a ratchet. There is one bolt in the center of the blade. Brace the blade with a block of wood to prevent movement. Loosen the bolt, remove the bolt and washers. Blade should come off easily now. Place your new blade in the spindle cradle and transfer the bolt and washers to it. Tighten with socket/wratchet.

It's that easy! Unless, the bolt is stripped, in which case the mower deck will need to go to a machine shop to get the bolt out.