How to redirect an old url to a new url?

You need to set up what are called 301 permanent redirects for each of the old pages. There are several ways to do this:

1) manually in your .htaccess file if you are comfortable doing that.
2) in your hosting provider’s control panel, if they offer that facility. This is often the easiest and most foolproof way and is offered by many hosts
3) using a WordPress redirection plug-in. This allows you to manage your redirects within the WP admin interface

Good luck.

ok, thank you. has someone an sample for setting this up in the .htaccess file?

Here there is a cool guide ??
https://www.seomoz.org/learn-seo/redirection

Plugin https://www.ads-software.com/extend/plugins/redirection/

has someone an sample for setting this up in the .htaccess file?

I linked to a guide on .htaccess redirects in #1 in my post above.

Thank you all!