Streamtime won't allow you to delete a Cost Matrix item that is currently being used in your database i.e. in an active Order, Quote, live task etc. You can only delete items when the job they are present on is locked. Editing a cost matrix item will trigger a message asking if you would like all instances of that item present in the system (against unlocked records) to be updated.
Before making changes, some housekeeping is recommended. Ensure all your statuses are up to date and all your completed jobs are locked. Any cost matrix items that you wish to phase out can be made bold (by right-clicking in the box). This does two things:
1. Any current jobs that are using that item can continue to do so without issue.
2. Provides a visual indication to anyone creating new quote/job items that the item should not be used (of course a conversation advising that bold items should not be selected would be needed).