some times i write somewhere in a site , eg i start a reply in a forum, and if i close the window konqueror warning me with a dialog box, that it has changes and if i like to discard them. By fault i checked to not be remind any more .
How can i return to the default value ?

There does not appear to be a way to do this through the user interface. If you are not attached to your Konqueror configuration, try removing $(kde4-config --localprefix)/share/config/konquerorrc

Otherwise, please post the contents of the above file here ( personal information removed if present )

thanks, i understood where i have to look :

/home/dimitris/.kde4/share/config/konquerorrc

and i changed this from false to true

[Notification Messages]
discardchangesclose=true