How to increase number of replicas after a bucket has been created


Using Couchbase 2.0.1, when I try to increase the number of replicas for a bucket, the drop-down list is disabled for some reason. Before upgrading to 2.5.1, I want to increase the number of replicas so I can remove 2 nodes at a time from our cluster for upgrade, not having to do each on individually. But to do this, the replica count on our buckets needs to be at least 2, currently all are set to 1. How can increase the number of replicas?