Answer 1

You simply activate the event to the container of your icons and when that event is activated you can remove the class that contains the first icon and then add the class that contains the second digit with some transition to make it look nice.
Another way to do it is to superimpose one icon on top of another, but one of them will have the empty display property, and once the event to the container is fired, you will remove that icon and hide the other.