Change date format from YYYY-MM-DD hh:mm:ss to YYYY-MM-DD

I have imported data from a database where the date format shows date and time. When I change the formatting to show only YYYY-MM-DD the cell shows the right format but if I select the cell it still contains the time (hh:mm:ss) and as I am using the value in a Pivottable and need to sort by date and find out how many times a day a truck has been loading, I need to get rid of the time stamp and only use the date. I am now using Excel 2010 but when I used 2003 I could use the function Left and 10 digits. When I try that now I get the built-in Excel numbers for the day and it does not work. Can anyone help me to get only the 10 digit date-format? How do I get rid of the built-in Excel day number?