How do you refresh a JLabel?

So I'm making a Java program for school and I chose to make a blackjack program. I'm making it so that the picture of cards will show up in JLabels and when the program starts, the dealer and the player has 2 face down cards. When the user clicks on a Jon, I want the cards to show a card value. Is there a way to refresh a JLabel? If not, how will I be able to change the picture from a faced down card to a face up card? Thanks in advance!