Hierarchical is the default clustering method, but the dialog enables you to switch to KMeans or Normal Mixtures. If you select KMeans or Normal Mixtures, when you click OK, a Control Panel appears where you can select any of the following as Method:
K-Means Clustering
See K Means Cluster.
Normal Mixtures
See Normal Mixtures.
Robust Normal Mixtures
Self Organizing Map
See Self Organizing Map.