how to animate different pic up weapons to the same character

I am making a game where the player selects a weapon from a list, how do I animate the character for each weapon, ie if 2 different characters use a knife and then one picks up a sword?

Do I change the character with a knife to the character with a sword? or is there a way to attach the sword to the character and take away the knife? or even just pick up a different knife object…