If a purchase order has been incorrectly received, you can un-receive the order if required.  To un-receive the order, click UnReceive PO from the received order's detail page.   The order will be reverted to the Approved state, ready to re-receive correctly or cancel. 

If there are stock controlled (FIFO, Batch, Serial) products on the order, this will reverse the stock movements created by the purchase order.  Note:  If un-receiving the order will put stock controlled products stock on hand into negative, the order can NOT be un-received.