change dates macro

Hi,

I need to create a macro that will change the date for me. Basically any date where the day is less than 10 or the month is less than 10 I need to swap the day and month round, in the format dd/mm/yyyy. i.e. 12/05/2010 should change to 05/12/2010 and 03/06/2011 should change to 06/03/2011.

I have a lot of files and even more cells to update so any help it much appreciated.

Thanks!