fonte:

3 Efficient Tools for WordPress Database Migration

e
https://codex.wordpress.org/Moving_WordPress

Moving a website and changing your domain name or URLs (i.e. from http://example.com/site to http://example.com, or http://example.com to http://example.net) requires the following steps – in sequence.

1. Download your existing site files.
2. Export your database – go in to mySQL and export the database.
3. Move the backed up files and database into a new folder – somewhere safe – this is your site backup.
4. Log in to the site you want to move and go to Settings > General, then change the URLs. (ie from http://example.com/ to http://example.net ) – save the settings and expect to see a 404 page.
5. Download your site files again.
6. Export the database again.
7. Edit wp-config.php with the new server’s mySQL database name, user and password.
8. Upload the files.
9. Import the database on the new server.

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ok, dopo aver bestemmiato tutte le pagine bianche che conoscete, sono provata ad andare al link dove avevo messo wp-migrate.php e non me lo faceva vedere, eprchè credo che cmq ha delle dipendenze su Wp stesso(che non stava funzionando).
Quindi ho rinominato la cartella htdocs in import-htdocs, ne ho creata un’altra con nome htdocs, ho messo un wp nuovo e prima di configurarlo sono di nuovo andata sull’indirizzo wp-migrate.php e questa volta me lo ha fatto vedere, da lì ho fatto lo scambio nomi delle url del nuovo DB. Poi ho ricambiato i nomi delle cartelle htdocs e il sito era perfetto come dall’altra parte!! yheee!

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When your domain name or URLs change there are additional concerns. The files and database can be moved, however references to the old domain name or location will remain in the database, and that can cause issues with links or theme display.
If you do a search and replace on your entire database to change the URLs, you can cause issues with data serialization, due to the fact that some themes and widgets store values with the length of your URL marked. When this changes, things break. To avoid that serialization issue, you have three options:

1. Use the Better Search Replace or Velvet Blues Update URLs plugins if you can access your Dashboard.
2. Use WP-CLI’s search-replace if your hosting provider (or you) have installed WP-CLI.
3. Run a search and replace query manually on your database. Note: Only perform a search and replace on the wp_posts table.