You can have named instances on the same machine with different version. You need to restore your database in the new instance. They are independent of each other. You can use SSMS 2014 (which most people are doing) to access both but you cannot access 2014 version database from SSMS 2012.
It is a good idea to keep a good backup. You cannot restore back your database from 2014 to 2012 easily. It is fairly easy to restore your 2012 version database to 2014 instance.