You can delete a task, without completing it.
Select the task to delete
Open the Tasks Popup to display the task list:
Hover the mouse over the task you want to delete, then choose Delete task:
You can add an optional note if desired.
When you're ready, choose Delete to erase the task.
Notifications and reporting
Depending on app configuration anyone assigned to the task, or watching the page will receive notifications to let them know of the changes. This configuration is set in the space and global administration guides.
Details of the changes will also be stored in the Activity Report - Content.