In spades all 52 cards are dealt out 13 to each player, so there's absolutely no way* to change anything in your hand. There's no deck or discard pile to draw from, unlike other card games were you can draw or otherwise pick cards up others have discarded/played, or some games even allow you to play cards off other cards already on the table.
*in some variants you can trade 2 cards with your partner if you are taking a nil
*in some variants you can trade 2 cards with your partner if you are taking a nil