If you want to delete a pending transaction, double click in the pending field and right click on the payment you wish to delete.  If the pending transaction is an ACH payment you will be unable to remove the payment until it posts to the loan and then can be reversed.

If the pending transaction is on the loan via ACH then you cannot delete the transaction.  If you need to remove this transaction then allow the transaction to post then reverse the transaction by using Reverse Payment.