Hi there Ineke,
It's important that your initial setup in a new company file is correct so that your books will start off well balanced. QuickBooks Desktop has the ability to import transactions and lists in various ways so that they can easily be entered into your books. I can provide some information about importing data.
One way you could start off fresh would be to import your chart of accounts as well as balances from an Excell format. This will allow you to start off the year with your previous data entered as opening balances. You can follow how to Export a report, this one being a trial balance, as well as how to import your chart of accounts from an Excel file by following the steps in this article about Importing and Exporting Excel files. You can find how to import the chart of accounts in the Standard import option. You can also import and export items, customers and vendors to help you keep those up to date in your new company file.
If you have any other questions, feel free to reach out here.
