In PSOhub, it is possible to delete a plan as long as no time entries have been booked towards the tasks.
Choose from the menu Plans and Plans.
Here, you will find all your plans. Click on the one you wish to delete to open it. Once in your plan, click the More button and then Delete.
PSOhub will now ask that you confirm this action that cannot be overturned.
Once you click Proceed, the plan will be deleted as well as the task lists and tasks associated with it.