The change in payroll financial year dates is to be completed once you have finalised your final payroll run and submitted your final STP.
To change the dates, you select Tools > Application Options
In the next screen, select the the + sign to expand the menu under Global
Once the menu has been expanded, select Payroll
Once Payroll has been selected, you will see your current payroll financial year dates displayed.
To change these dates, you overwrite the current dates with your new dates and select Save ( located at the bottom of the screen ).
This completes the reset of your payroll financial year.