To delete all tasks do the following:
1. Log out the software on all of your devices.
2. At the Windows version activate the Work offline point of the main menu.
3. In the main menu — Database click the Clear Database point of the menu.
4. Enter your personal account at leadertask.net and at the account properties page click Clear data on Server.
5. At the Windows version deactivate the Work offline point of the main menu.
Notice, that you can only complete tasks assigned to you (set them the Awaiting Approval status to hide them this way). Only creator of these tasks can delete them.