The answer is the following:
C:\> SqlLocalDb i
v11.0
C:\> SqlLocalDb stop "v11.0"
C:\> SqlLocalDb delete "v11.0"
References: http://www.mssqltips.com/sqlservertip/2694/getting-started-with-sql-server-2012-express-localdb/ and http://www.codeproject.com/Questions/542249/CanplusnotplusRunplusAzureplusApplicatioinplusGetp"