The beginning of a fiscal year cannot be changed unless you create a new company database..
The end of a fiscal year could be changed in fiscal calendar, providing that the periods dates are adjusted accordingly. However changing the fiscal year end would affect certain reports that report by period. These reports may not be accurate when report for periods that are not a full month.
There is also a 3rd party product from Code Partners which allows you to modify http://www.codepartners.com