Upgrade SQL Server 2014 Failover Cluster to SQL Server 2016 Availability Group on Windows Server 2016 In our current set up we have 2 node SQL failover cluster in data center DC1 with mirroring enabled. And similarly in DC 2 a 2 node SQL failover cluster. DC1 acts as primary via DB mirroring in one point of time and DC2 mirror.
 Above runs on Windows server 2012R2

How can I convert the above setup from sql cluster to get cluster so that can leverage always on. I know this is sort of s big question but needed to know how can this be achieved with some overview and I can do some poc on that. We are thinking to upgrade to sql 2016 on Windows 2016 if possible.

Please guide for any real time experiences or blogs I can go through to do such migration.

Edit-- Per Answer below which needs the DR server at different DC to be out for route seems to be last option but i will still test to figure out the timings.

Also, is it possible to have setup like configure LS on current prod server with 4 node new built multi site cluster for alwayson AG? And during cutover we can simply stop the LS job on prod and convert the LS secondary on 4 node cluster to alwayson AG configuration
To migrate from two Failover Clustered Instances (FCI) to an Availability Group (AG) that spans four Availability Replicas is fairly straight forward but somewhat of a lengthy process. Also, some downtime is required to point your application to the Availability Group Lister and manually fail over to one of the Secondary Replicas.

This is a high level overview of the process so use the links provided to plan:


Disable Database Mirroring
Completely uninstall the FCI and destroy Windows Cluster at DC2


Uninstalling a SQL Server Clustered Instance

Install Standalone SQL Instances on the two nodes at DC2
Join the two new stand-alone servers at DC2 to Cluster at DC1 and configure the AG


Combine a failover cluster instance and Availability Groups
Configure Availability Group on a multisubnet cluster

Take down time to fail over to to a Secondary Replica in DC2 and update Application to point to Listener
Remove FCI from AG


Remove a secondary replica from an Always On Availability Group

Completely uninstall the FCI at DC1
Repeat Step 3 at DC1
Add new stand-alone instances to AG


Add a secondary replica to an Always On Availability Group



All of this can be done on SQL Server 2014. There are some benefits to upgrading to 2016 but I would recommend you read this to help plan as there are a lot of similar steps to upgrade.