I recommend setup a new Exchange server with SFW-HA clusters and migrate your users to it. By doing this you will be able to test the new Exchange cluster and ensure that it is working completely before you start putting production users on it. It also gives you the out if things are not working correctly then you just migrate your users back to the existing MSCS Exchange cluster.
You will need to leave the MSCS Exchange cluster up and running for awhile after you migrate your users off of it. The reason for this is to get your users to automatically switch to the new Exchange server. Clients that use Outlook or Exchange clients will automatically be redirected to the new Exchange server the first time that they log in after their mail box has been moved. This is a big time saver in reconfiguring all of your clients.
Follow the VCS Exchange solutions guide on how to setup a new Exchange Server cluster.