@stevee1
You may consider these steps:
1. Install the trial license of QBD 2015 on your current machine and convert your company file on it.
2. Prepare your new machine with Win 8.1 or 10.
3. Install the trial license of QBD 2020
4. Create a backup file on the old machine and restore it on the new machine.
5. Purchase the one time license of QBD 2020 and activate it. Make sure you have a free upgade option to QBD 2021 if you purchased within this month.