How to Format Excel 2007 Date and Time value in Huge Database?

I currently have huge Excel 2007 data bases (> 100K rows) that have three columns Date Created, Date Modified, Date Last Uploaded. Each of the cell values under each Column displays a value such as 7/1/2001 12:00:00 AM. I need to be able to easily remove the time value from each cell and format the cell to a date format that I can easily sort. Any ideas on how to do this? I greatly appreciate your help.