Most other popular browsers have a reset option that allows you to reset the browser to it's original settings, but Opera does not include this option. If you want to reset Opera, you have to do it manually.
1. Type 'opera://about' into the Address bar and press Enter 2. Look for the Paths section and remember the 'Profile' and 'Cache' locations 3. Close the Opera browser 4. Navigate to each of the locations from the Paths section on your computer 5. Delete the 'Profile' and 'Cache' folders from these locations
Next time you open Opera, everything will be reset to it's original settings like you just did a fresh install.