You should start a new financial year only when all the transactions and balances have been finalised for the current financial year. This is because once a new financial year has been started, you cannot make entries in the closed financial year.
Take a backup of your data file (File menu > Backup). Store your backups securely. If you want to view your transaction data in the future you will need to be able to restore this backup.
Go to the File menu and choose Start a New Year. The End of Year Rollover wizard appears.
Follow the prompts that appear in this step-by-step process.