For made reservations of Customer Order Lines, Shipment Lines as well as for Shipment Order Lines it is possible to do un-reserve. Un-reserve means that the reserved parts are released from reservation and will be available for reservations or picking, etc. by other demands.
Reservations may be un-reserved or changed at any time until a pick list has been generated. You can perform these actions for inventory parts. Manually un-reserving a reservation for one or more order lines in the Customer Order Lines or Customer Order page works the same as un-reserving in the Manual Reservations for Customer Order Line and Manual Reservations for Shipment Line pages.
If you no longer want to pick and deliver the entire reserved quantity, it is possible to change this in Manual Reservations for Customer Order Line or Manual Reservations for Shipment Line page. For inventory parts, query for the source object in question and enter the required quantity in the Reserved Qty field in the lower part of the page. Save, and the quantity you do not want to pick is no longer reserved. Save when completed. For handling units you can un-reserve already reserved handling units and then reserve new ones - note that this is done for complete handling units and all of its content. Partial reservation of a handling unit needs to be handled per part and quantity.
Note that you cannot manually reserve material on created transport tasks, however you can manually un-reserve material on created transport task.