Can I change a Layby sale to an On Account sale or vice versa?
No - once a sale has been processed as a Layby or On Account sale, it cannot be changed to another type of sale.
You need to void the sale and recreate it as the correct sale type.
Steps that needs to be followed in order to recreate the sale as a 'On Account' sale:
Step1: Voiding the original sale:
Step 2: Recreating the sale to change the sale type: