All users (except for collaborators) with whom the task is shared can delete the recurrence.
Open any task that's part of the recurrence in Task view.
Click the task’s three-dot menu button in the upper right-hand corner.
Select Edit recurrence from the drop-down menu that appears.
Click Delete at the bottom of the pop-up that appears.
New recurrent tasks will no longer be created, and all tasks in the recurrence sequence that weren't manually edited are deleted.