I linked a bank account to my Odoo instance but I wasn't ready, as I had a lot of test data but had not yet imported my real data.  I first had to delete all the imported transactions, as described here: 

https://www.odoo.com/es_ES/forum/ayuda-1/how-to-delete-banking-entries-journals-222003

However I wasn't able to follow those instructions to delete the bank account connection.  I was sent these instructions from a ticket I opened and it worked perfectly:

"To delete a bank account synchronization, you'll need to access the configuration menu, but this option is only visible if developer mode is active."

Here are the steps to activate developer mode and delete the bank account synchronization:

1. Activate Developer Mode:

 - Go to the Settings app in your Odoo database.

 - Scroll to the bottom of the page.

 - Click on "Activate the developer mode."

2. Delete the Bank Account Synchronization:

 - Once developer mode is activated, go to Accounting > Configurations > Online Synchronization.

 - In this menu, you should now see a list of linked/connected bank accounts.

 - Select the bank account you want to delete.

 - Choose the "Delete" option to remove the synchronization."