European airlines do not allow standby for earlier flights in the same way that US airlines often do.

For the paid ticket, a change would only be allowed if the conditions allow for it (i.e. it's a fully flexible/changeable ticket). If there's any sort of change fee, KLM would likely charge that fee to move to the earlier flight.

For the award ticket, it will depend on whether award availability is available for the earlier flight. If yes, it would be free of charge on a flex award, or EUR 45 on a classic award.