Upgrading an instance of SQL Server isn’t always easy, but it SQL Server 2012 and 2014 have the features to make it worth your time and effort. Here are some basic post-upgrade tips for avoiding issues.
After your upgrade, monitor any applications that access the database server looking for performance issues, and review Windows and SQL Server error logs to validate that there are no issues. You should also rebuild all user databases indexes and run sp_updatestats to update statistics against all internal and external tables.
In addition to these simple tasks, execute DBCC UPDATEUSAGE against all user databases. This will correct page and row counts in the catalog view.