Offline mode
When working offline, data can be deleted locally by opening the "About" window, 
scrolling down and clicking "Remove local data" label.

Note: the data cannot be restored!

Online mode
When working through Auth and storing data on the server, the data is deleted with the same way. 

All data will be deleted both on the device and the server, and the account also will be deleted.
Note: the data cannot be restored!