I entered several invoices that should have been entered as estimates, is there a way I can change them without having to delete them all and start over?

Welcome to the Community forum, cateringbythelake.

At this time, changing the invoice to an estimate isn't an option. You can enter batch transactions in QuickBooks Desktop for the checks, deposits, credit card charges and credits, bill and bill credits, and invoices and credit memos. 

So for now, you may need to delete the invoices created and manually enter an estimate transaction again. 

To get started, make sure that the Estimates feature is turned on. Here's what you'll need to do:

1. Go to the Edit menu at the top, then click Preferences. 
2. Select Jobs & Estimates in the left menu and go to the Company Preferences tab.
3. Choose Yes to the question "DO YOU CREATE ESTIMATES?".
4. Click OK. 

Once the Estimates feature is turned on, you can now create an estimate. To complete the process, follow the below steps:

1. Go to the Customers menu at the top, then click Create Estimates.
2. On the Customer: Job drop-down, select a customer or customer job.
3. Fill in the necessary information. 
4. Click Save & Close.

You can visit this article for a more detailed step by step process: Create an estimate.

For your future reference, I'm attaching some articles below that you can find helpful:

• Set up and send progress invoices in QuickBooks Desktop
• Some Sales Orders or Estimates may be incorrectly marked as closed

You can get back to me anytime you have additional questions in QuickBooks by posting your response below. I'll do whatever it takes to ensure your concerns are addressed. Have a great day.