QB has changed my default sales tax and an old rate is showing - how do I delete/remove it so it doesn't show any longer

You can remove the old tax rate by making it inactive, cdemuri. Let me guide you with the process.
 

When you use the automated sales tax feature, QuickBooks automatically generates the tax agencies and sales tax rates you need. In your case, we can make it inactive so it will not show in your taxes. 

Before doing so, you cannot reactivate a tax rate. If you need it for future use, you’ll have to create a new one. To do so follow the steps below:

1. Go to Taxes, then select Sales tax.
2. In the Sales Tax Center, click Sales Tax Settings.
3. Choose the tax rate name, then tap the drop-down arrow and click Make inactive.

However, if you need to use the tax rate, you can manually edit the sales tax. Here's how:

1. Go to Taxes, then select Sales tax.
2. Select Sales Tax Settings.
3. In the Custom rate section, find the sales tax rate and click Edit.
4. Update the rate accordingly and click Continue.

For more details, about the process above, open these links:
 

• Delete sales tax rates and agencies in QuickBooks Online
• Edit sales tax rate in QuickBooks Online
   

Also, I'll be adding these links to know how tax rate is calculated and get a detailed look at the taxes you owe in QuickBooks:

• Learn how QuickBooks Online calculates sales tax
• Check how much sales tax you owe in QuickBooks Online

It would always be my pleasure to assist you, whether it's regarding sales tax rates or any other QuickBooks-related concerns. I'm always here to lend a helping hand. Take care.