Upgrade Distributed vSwitch from 5.1 to 5.5

When you upgrade your VMware environment to version 5.5. remember to upgrade your distributed vSwitch as well; it will not be done automatically. In this way, you can utilize new features in dvSwitch 5.5, including:

The upgrade process is fairly easy and the good thing is that according to VMware documentation, it is non-disruptive which means there is no outage and no host and VM will get down or experience issues. Find your distributed vSwitch either in vSphere Client or Web client, right click and do upgrade.