Excel 2007 change date format

Hello,

Currently my excel spreadsheet shows m/dd/yyy (example 9/15/2012). I would like it to show dd/mm/yyy (example 15/09/12). Is there anyway to do this without re-typing everything? I have selected the dates and tried to format the cells to "date" (before they were just showing "general") but it is not working.

I tried =TEXT(A1, "dd/mm/yyyy") but I must be doing something wrong because it just keeps the format at 9/15/2012.

Help! Thank you!