I would like to change the REF NO TYPE from Deposit to Sales Receipt for a number of historical transactionsIs this possible?

You'll want to change the reference number directly from the sales receipt, angelo3.

Changing it from the deposit page will not affect the reference no. shown on the sales receipt. Just open the sales receipt and change the no. manually.

Check these articles for future reference:

• Enter historical information
• Customize your invoices, estimates, and sales receipts in QuickBooks Online
• Process a credit card payment in QuickBooks Online

Stay in touch if you have any other questions, I'll be happy to help you out.