Moving All SharePoint Databases to a New Database Server

Using backup and restore. Here is the procedure from Steven Haden's Blog:

1. Using the SharePoint Central Admin, make a full backup the whole farm.
2. Start the SharePoint Products and Technologies Configuration Wizard and disconnect the web server from the farm
3. Using the SharePoint Products and Technologies Configuration Wizard define a new farm in the SQL server, that creates a new configuration database
4. (Updated) Using the SharePoint Central Admin restore the full backup in your new farm, running it twice. Select New configuration to be able to change the Database name.
1. Restore first the content database
2. Restore the SSP and its content

Or this article from TechNet:

Move All Databases

When building a new farm, we should consider using sql connection alias to add a layer of abstraction between SharePoint servers and database server.