The steps are the same, as in the 2010 world.
As in Exchange 2010, installation of 2013 Mailbox role creates a new mailbox database with a name “Mailbox Database *”, where * represents a long number. Exchange administrators prefer to follow a naming convention and keep things clean.
Easiest will be to rename the default database to something that suits your naming convention. Click the Edit button and rename the database & hit the Save button.
--> Please see the rest on the blog : http://www.howexchangeworks.com/2012/11/how-to-tackle-the-default-database-in-exchange-2013.html