How is ne world transferred to a higher version?

I would like to start minecraft hardcore again but i'm afraid that if a new version comes the world will be destroyed when it is transferred and i have to stay with the old version or start new ones

What you have will remain, but the transition to the new biomes will probably have such edges:

And if you intend to play in snapshots (= developer versions): be careful. Something can break. Always make a backup of your world beforehand.