Mac: Locating wp-themes directory

BlueHost is hosting my domain and allowed me to automatically install WordPress files. I am now trying to change my theme by FTPing my desired theme into a “wp-themes” directory. However, I can’t seem to find a directory named “wp-themes”. Can anyone advise on where my wp-themes directory is? From what I am reading, it should be easy to find – but, I must be missing something.