why do the men die again ? did they ever change ? what has happened to the curse ?

When you say "die again", what part of the poem are you referring to?

The men died only once. When they "became zombies" it was because angels in habited their bodies so they never actually came back to life to then die again. The curse was lifted when the Mariner showed love and compassion for the slimey water snakes, which was the lesson in all this. The love which should bind together all living things.