European airlines won't just change your flights for free - unless it helps them too, such as if your original flight was oversold and they would need to offload some pax anyway. Given that you want to move to a more expensive, and hence busier, flight - that seems unlikely.

Expect to be asked for further payment if you do enquire. However, having checked-in luggage already in transit means that asking to move when you get to Amsterdam is already too late.

Not sure what the situation is now, as the airport is being rebuilt, but there used to be lockers airside as well as landside.
http://www.schiphol.nl/Travellers/At...ageLockers.htm