Before we start, may I know what you want to do with your recorded transactions in QuickBooks Online? Any additional information would help. Also, in terms of changing the categories, I suggest reaching out to your accountant before doing the process to avoid future discrepancies.
If you are trying to delete a transaction, here’s how:
In your QuickBooks company, go to the Accounting tab and select Charts of Accounts.
Click the View register along the bank you need to modify.
Click on the transaction, and click Delete then confirm.