How do I move a transaction from one account to another?
Select a transaction in any account (or Command-click to select more than one), then choose Edit > Cut. Select the account to which you want to move the transaction(s) and choose Edit > Paste. The transaction(s) will be removed from the original account and added to the selected account. Be sure to use the Cut command and not Copy, to ensure that transfers remain properly linked and are not duplicated.
To transfer cash between accounts (instead of moving the transaction records), see Account Transfers.