How do I reverse a posted Journal Entry?

To reverse a posted journal entry, you will need to debit and credit the opposite of what was originally recorded.

Using the below entry as an example, to reverse this you would record a new journal entry via Accounting > Journal Entry > New Journal Entry as follows:

1. Credit (-) -5.00 to Citi Bank Account 
2. Debit (+) 5.00 to  Retained Earnings Account