During Rental

How can I add additional insurance packages? Can the vehicle be returned before the time stated on the contract? How do I add an additional driver to my rental contract? Can I rent GPS, Wi-Fi or child seat? Can I return the vehicle to a different location than the one stated on the contract? How do I prolong the rental period? If there is a problem with the car or a traffic accident, or if I lose the vehicles documents, licence plates or keys, what do I do?