How do I change a default animation while it's playing?

I know how to change a default animation, however if I change one while it's playing, (for example changing the running animation while the player is running) it won't use that new animation until the current one stops and starts again. (for example to stop running then start running again)

Does anyone have a solution for this?

You mean you changed the AnimationId of the object Animation? You could add a .Changed to the animation and bind it to a function that stops the animationtrack (You can also go to your humanoid and :GetPlayingAnimationTracks() to stop() all animations currently playing) you played and starts a new one.