I have a number sequence that is back to front & want to represent this in the standard European format e.g..
2009-08-24 should be 24/08/2009
There are several thousand date records to change

How do I do this?

Are the cells formatted as dates or text?

If the cells are already formatted as date, you can simply highlight the cells and press CTRL-1 to open the cell formatting wizard and apply a Date format of your choosing.

If the cells are text strings, you can convert them to date strings with a simple trick:

1) Highlight the date cells in a single column
2) Select Data > Text To Columns > Delimited > Next > Next
3) On the 3rd screen of the wizard, click on DATE: YMD in the upper right corner
4) Click OK

The cells now have standard date strings in them and you format the cells to display any way you wish.

The Date is a number sequence without separation characters e.g.. 20051025 = 25 Oct 2005

In that case use the STR() function to convert to a string and then use the Mid function to parse out the components.

Actually, the trick proposed in post #3 will work on text strings like this, too. Just pick YMD so Excel knows how to evaluate the string.