What would be the process to Upgrade a SQL Server 2012 Ent. Act/Pass Failover Cluster to a SQL Server 2014 Ent. Failover Cluster

Hi,This is my current scenario:Windows Server 2008 R2SQL Server 2012 Enterprise Edition Active \ Passive Failover ClusterIntended scenario: Windows Server 2012 R2 MS SQL Server 2014 Enterprise Edition Active \ Passive Failover ClusterBased on this what do you recommend as the procedure?1- In place - OS upgrade2- In place - SQL UpgradeWill above steps be a feasible option?Thanks in advanced for your comments