Attempting to Alter an Excel Gantt Chart into Monthly Gant Bars - Please Help!

Hello All,

I have been using an excel based Gantt chart that I want to marry up with a cashflow, however I would ideally like to be able to have the Gantt chart populate in Months (Start Date - End Date = Duration). In the attached sheet it performs this function by weeks however I do not know how to alter this to manage it in months ie. Jan 13, Feb 13 etc.

Please can someone advise how to alter the sheet to achieve this?

Many thanks!

Chris