How do I move a transaction to a different account?

A transaction can be moved from one account to another by taking the following steps:
Right click (or Ctrl + Click on a Mac) on the transaction and select "Batch Change->Account", then select the account you want to move the transaction to.

If you want to move more than one transaction at a time, you can highlight multiple transactions by either Shift + clicking (click the first transaction you want to move, then hold shift and select the last one, thereby selecting all the transactions between the two clicked) or Ctrl + clicking (select multiple transactions by holding Ctrl and highlighting or unhighlighting the transactions), then right click and go to Batch change -> Account and select the account you want to move the transactions to. The two clicking methods can be combined, by the way, so if you have a very large block to go to a new account with one or a few transactions to stay, you can Shift click the large block to highlight them and then Ctrl click the ones you want to unhighlight.

Please note: it's not possible to move transactions to or from Investment accounts