Remove "empty" exchange 2010 installation from domain and replace with Exchange 2013

I had one Exchange 2007 server that I wanted to upgrade to 2010.  I was (apparently incorrectly) advised that installing Exchange 2010 would have no impact on my existing environment.  But when I decided to install Exchange 2013 instead, and tried to remove Exchange 2010, I was surprised to see that when I went to recipient configuration that every mailbox from the Exchange 2007 mail server was there (albeit it says "database copy").  When i tried to uninstall Exchange 2010, the setup program halted and said Mailboxes were present??  Given the situation, how do I break any connection between Exchange 2007 and 2010 and get it uninstalled without affecting users (who currently all point to Exchange 2007 for email?).  THanks.