I think it depends on why you are doing it. You can pause a node so that no resources can be used on it (perhaps to perform maintenance on that node) or you can evict a node so that it is no longer part of the cluster (maybe because that node has died). You can't convert a clustered SQL Instance into a non-clustered instance.

If you want to permanently remove SQL from one of the nodes you can do that via the SQL Setup on the affected node.

To do evict or pause a node, you go into the cluster administrator on the nodes section and right-click to select the desired option.