i want to keep the day constant but increase the month by 1 in every cell how

ex 27/01/2014, 27/02/2014, 27/03/2014 etc

Enter two dates into two cells, like 27/01/2014 and 27/02/2014, then select both cells and pull them down at the bottom right handle.

Or enter just one date 27/01/2014 and select a cell range including that cell at the top and invoke menu Sheet → Fill Cells… → Fill Series…, Series Type Date, Time Unit Month, Increment 1.