Script to run SQL upgrade to 2012 unattended

I need a script to run silent and unattended to upgrade from 2005 to 2012. Backup the SQL databases, remove SQL 2005, Upgrade to 2012 and attach preexisting databases to the newly upgraded 2012. I've noticed that when upgrading to 2012, there are two instances of SqL ( both 2005 and 2012) sharing the same databases, hence creating a lag time in production. This is needed for an upgrade of around 1000 sites. Thank you