Deleting a Decision Table 
The delete option is only available for those decision tables created in the rules manager. You cannot delete a decision table :
After you upload the changes made to the decision table.
For more information, see Uploading Changes
If it is being used in a rule. More Information: Using a Decision Table in a Rule.
Procedure
In the Rules Navigator view, expand the project node and select the ruleset or flow ruleset.
Under the Decision Tables section, select the decision table.
Choose the Delete button.
In the dialog box that appears, choose OK.