Morning!
Unfortunately, the application cannot clear your stats, since it is saved on the Valve servers.
What you can do, is to use the "Edited stats" function (right click on any number to edit it), or (in the settings window), press "Reset stats" to empty all values.
However, this will only change the numbers displayed inside the application. We can't do anything about Valve's numbers on you.
Kindest Regards,
Erlend Dahl