To Convert QuickBooks Desktop to Online, start by signing into QuickBooks Online. In QuickBooks Desktop, go to the "Company" menu and select "Export Company File to QuickBooks Online." Follow the prompts to sign in again, and choose the online company to import the data into. Review your data in QuickBooks Online to ensure everything is transferred correctly. Additionally, it's wise to back up your QuickBooks Desktop data before starting the conversion. Lastly, consult QuickBooks Online support or a professional accountant if you encounter any issues during the process to ensure a smooth transition.