Change mapping without losing data


Is it possible change mapping without losing the data?


You have to reindex. Have a look at the reindex API.

It's my first production project with elastic and maybe my questions could sounds stupid.

It is very interesting, but doesn't it introduce some overhead to the search instead of making the request to the original index?

Another question, how can I export data from my elastic server and load it to another elastic server?


If you need to change the mapping, you must reindex. Reindex can mean reindex in place or in another index (which I prefer).
No search overhead because it will be a fresh new index.

To copy from one server to another one, reindex API or snapshot and restore if you don't need to change the mapping