This quorum configuration can be changed using the Configure Cluster Quorum wizard. This wizard can be started from the Failover ...

This quorum configuration can be changed using the Configure Cluster Quorum wizard.  This wizard can be started from the Failover Cluster Manager console by selecting the cluster name in the left hand pane, then in the right "actions" pane selecting "More Actions..." and then selecting "Configure Cluster Quorum Settings...".