Default Currency Format

Hello. My colleague and I both downloaded an Excel workbook from a share point site. In the column containing currency, our formats were different. For negative one-hundred dollars, my format was -$100.00 whereas his format was ($100.00). I'm assuming that this format is set by some default setting at the computer, MS Office or Excel level. We need to change his default format because he will be receiving these workbooks all the time and they are used as input to an automated reporting system. How can this be done? Thanks.