1. Go to System Settings -> Shortcuts -> Global Keyboard Shortcuts -> Plasma 2. Change shortcut for "Activate Application Launcher Widget" to Ctrl+` 3. Logout 4. Log in Shortcut has backed to the default which is Alt+F1
See bug 300532 comment #24 for the procedure to change Plasma shortcuts. *** This bug has been marked as a duplicate of bug 300532 ***