If you want to delete an activity first open the Administrator's overview of the activities in the sidebar Activities | Items.
Select the item you want to delete from the list. If you have difficulties finding your activity please read this article.
If the item is recurring you will be asked to choose between only editing one particular instance of that activity or edit all the instances of that article:
Choose what is appropriate for you.
Once an activity has been changed "just once" the connection to the recurring activity is severed. Changes made to the recurring activity will no longer be applied to that particular activity.
After you open your activity go to the status (under the picture of the activity) and press 'pencil' button to change the status.
To delete an activity please use 'archived' option as a new status.
After finishing editing an activity do not forget to save your changes.