As long as no transactions have been posted to the account you will be able to delete using the following steps:
Click the relevant ledger (Sales Ledger, Purchase Ledger or Nominal Ledger), then click the relevant option (Customers, Suppliers or Trading Partners).
Locate the account, then click the relevant tab (Customer, Supplier or Trading Partner).
Right-click and select Modify Record.
Right Click and select Delete Record.
Select Yes to confirm deletion.
Go to the Details tab for the customer or supplier.
Right-click and select Modify Record.
Right Click and select Delete Record.
Select Yes to confirm deletion.