Different Costumes[C#]

I am working on my first 2D game. Something I'd like to be in it is some sort of currency that the player get and spend on another costume for the default sprite the player is playing as. Im not worried about how to add the currency to be picked up into the game, but rather how to go about the change of sprite mechanic itself. I want to have the selection in another UI Menu where the player pays a certain amount of currency to get a random Costume. I have no idea on how to approach this mechanic because I'm still really fresh in the unity scene. Any insight would be appreciated!