If the baseline is a test baseline, do not publish it.
If the task is in a published baseline, you will need to mark that baseline for deletion.
Right-click over the baseline and choose Delete. The Delete dialog box displays and informs you that you are marking the baseline for deletion.
Only the CM Administrator can delete a baseline marked for deletion. However, if you mark a baseline for deletion and your CM Administrator has set up a command to automatically delete all baselines marked for deletion, then the baseline will be deleted. Be sure that you want to delete a baseline that you mark for deletion.