1. Log in as sysadmin. 
   
2. Switch to Single-user mode if in multi-user mode.
3. Go to Setup, then Settings.
4. Select Company, then Information.
5. Enter the new date in the Fiscal End field.
6. Click OK.

 NOTE: You can't set the fiscal end date earlier than the latest transaction date.

The fiscal year end date can’t be changed
Error: "Invalid date. The Fiscal End date must be later than or equal to the Latest Transaction date."
What is the sysadmin password?