It would be best, if you create new Databases and get rid of the default database on Exchange 2010. But this is tricky as if you try to remove the database it will tell you that there are still items left in the database, therefore you cannot remove it. But if you read through the error message, you will find the commands you can start the cleaning up process with.  Please use Exchange Management Shell to do these steps:

1. First get the names of the mailboxes sitting on your default database by running:
   Get-Mailbox -Database “<your default database name>”
   This will give you a list of mailboxes sitting on your default database. All these mailboxes can be easily removed using Exchange Management Console.
2. Even after moving those databases, you will still not be able to remove the default database, as there are still some system mailboxes sitting on the default database. Follow these steps to remove them:
   1. Get-Mailbox -Database “<your default database name>” -Arbitration
      This command will show you all the system created mailboxes. If you cannot see the full name of the mailbox try this command
      Get-Mailbox -Database “<your default database name>” -Arbitration | fl
      You can also try:
      Get-Mailbox -Arbitration | Where {$_.Name -like “SystemMailbox*” } | ft –wrap
   2. Create new mailbox move request for all those system mailboxes, for instance:
      New-MoveRequest -Identity “SystemMailbox{<your unique guid>}” -TargetDatabase “destination database name”
      New-MoveRequest -Identity “SystemMailbox{<your unique guid>}” -TargetDatabase “destination database name”
      New-MoveRequest -Identity “FederatedEmail.<your unique guid>@<your domain>” -TargetDatabase “<destination database name>”
   3. Check the status of the move requests using:
      Get-MoveRequest
      Check the names under “DisplayName” as you will use this name to clear the move requests in next step.
   4. Once Exchange has finished moving the mailboxes, you can clear those move requests using:
      Remove-MoveRequest -Identity “Microsoft Exchange”
      Remove-MoveRequest -Identity “Microsoft Exchange Approval Assistant”
      Remove-MoveRequest -Identity “Microsoft Exchange Federation Mailbox”
3. Now you should be able to remove the default database, make sure you browse to that file location and remove the .edb file manually as well.