@Natashca 

You may have 3 options:

1. Buy a 3rd party conversion service. Contact me in private for details.

2. Use a migration tool (i.e TPExporter for Desktop and TPImporter for Online)

https://get.transactionpro.com/qbo

3. Keep your historical data on QB Desktop and start from scratch on your QB Online. You can buy a 3rd party service to migrate CoA, Lists, and Beginning Balance only to lower your cost. Contact me in private for details.