Excel 2013 - change back to original selected cell border

Hi

I have a client who has just upgraded to Office 2013. The other day they asked if it was possible to change the look of a selected cells border. In previous versions it was a thick black border around a selected cell or range of cells, in Excel 2013 it's a thin green line and it's not so easy to see. Is there any way to revert back to the think black line?

Hope this makes sense. I don't' want to put a border around a cell I just want a selected cells border to be like the old version.

Thanks, Viv

Viv Haig