Locate the ruleset (Where is my ruleset?) and in the Outline view, choose the Definitions node.
In the Definitions Editor that appears, under the Fixed Definitions or Variable Definitions section, select the definitions you want to delete as shown below.
Press Ctrl + D or Delete
In the Delete Operation dialog box that appears, select the definition you want to delete and choose OK.
Note
You cannot delete a definition if it is being used.