How do i chang a freeze plug 94 chevy astro?

If you have clear access, drill a hole in it, they are soft, stick a screwdriver big enough for the job, pry it out. Clean the surface, get a new one, same size tap it in, done deal. truth is most of the ones that go out/leak are not very accessible, you may need to raise the engine or do whatever it takes to get at it.