Renewal of Essential Support for Backup Exec 2012

I would like to renew the Essential Support for my Backup Exec 2012. However, I can only purchase support of Backup Exec 2015. Isn't it possible to downgrade the essential support license to Backup Exec 2012 after purchase?

Also, can I upgrade to latest version of Backup Exec after downgrade but within the essentail support period?

Thanks and Regards,

Jeff