How do I change a customer name on a paid invoice.

You can go to that paid invoice and update the customer name, @dakis528.

Check the following steps:

1. Go to Sales from the left menu and click on All Sales. 
2. Find that invoice and click to open it.
3. Update the customer name.
4. Click the Save button once you're done.

Here's more information on how to record invoice payments in QuickBooks Online. 

I'm always here if you need further help with your invoices. Let me know in the Reply section below. Have a great rest of the day!