I started a survey with Google form. Everything is fine. But one Answer was accidentally given twice. As I understood, there are two locations of the answers. Internal, of the form and a copy of each answer is sended to a spreadsheet. Deleting a single Row in the spreadsheet has no effect to given answers from the form. So, how can I delete a single entry of that form answers? Any suggestions?
The answer that this wasn't possible by @ruben was true until very recently.
This is now possible on the New Google Forms. (Google announcement on the 10th of February 2016).
The New Google Forms allows you to delete responses from within a Google Form.
To delete individual responses you click on the "Responses" tab and choose "Individual". You locate the record you wish to delete and click on the trash can icon to delete that individual response.
Make a note however that the response/s will NOT be deleted from the connected to the form spreadsheet (nor will any files they had to upload as part of the form).