How Can I Remove The Workitem Type From The Existing Project?

When creating a new project using 'Agile' process template, there are 5 workitem types in the list of workitem type by default. After the project being created, how can I delete some workitem type that we don' t need?



For example, my team will never use 'Senario' workitem type for the project and I would like to remove this workitem type from the list. So no team member will see 'Senario' workitem type in the list when creating workitem, and therefore no one will create a workitem using 'Senario' workitem type by accident.



I understand that workitem type can't be deleted if it is used to created any workitem. So what I mean is the workitem type that has never used to create any workitem.



Thanks.