You can batch delete unallocated cash on the Money > Unallocated cash menu using the feature at the top of the menu. 

Click on the down arrow to expand the options.

This process includes the deletion of unallocated cash which is partially allocated to invoices. However, unallocated cash which has been included on a VAT return will not be deleted. 

The batch delete unallocated cash feature allows you to delete multiple payments in a payment ID range. 

All payments have a payment ID, the payment ID for any unallocated receipts and payments is also shown on the Money > Unallocated cash menu under the Payment ID column of each respective table.

In this case, I will be deleting the two unallocated receipts. 

Using the batch delete feature at the top, my Payment ID will begin with 1685 and end with 1778. The Type is set to Receipts only.

Only unallocated receipts (not included on a VAT return) in this date range will be deleted. Technically the range, in this case, could, in fact, begin from 1 and end in any number after 1778 as there will still only be the 2 unallocated receipts I want to delete. 

Hit the Delete button to continue.

You will then need to confirm the deletion by hitting the Delete button again.

Please be aware that this is a permanent process and you will not be able to restore the deleted payments.