The context menu for Stage Table objects, listed in the left pane provides an option for maintaining Data Vault hash key columns. 
You can review the composition of existing hash keys for a Data Vault Stage table (Hub, Link, and Satellite) and create additional hash keys by selecting the Maintain DV Hash Key Columns option from the selected Data Vault Stage Table's context menu. This launches the hash key generation Wizard which enables you to maintain the source columns defined for the hash keys. Refer to Creating Data Vault Stage Tables for details.
To remove or change a hash key column, you need to delete it first, e.g. right-click the column listed in the middle pane and then select Delete Column from the context menu.