I am implementing a ranking system based on the Elo rating and cannot get a point about the K-factor. If two players with different skills and, therefore, different K-factors are playing, which exactly K-factor should be used when changing their ratings?

For example, player A has rating 2500 and K-factor 16 (probability ~75%) while player B has rating 2300 and K-factor 24 (probability ~25%). If player A wins, do I need to use 16 as K-factor for both players or 16 for player A and 24 for player B?