Load sprite from asset (from asset store) at runtime

I "bought" a free asset with icons (it includes the ".png" files) in the asset store and want to change the sprite of a button from one of the icons to another when I click on the button.

I know that you can load a ".png" file from the "Assets/Resources" folder like this:

myButton.GetComponent<Image>().sprite = Resources.Load<Sprite>("PathToFile");

Is it possible to load the icons from the asset's folder that was created when I downloaded it (the path's something like "Assets/IconAsset/128x/icon1.png") at runtime or do I have to copy the files I want to "Assets/Resources" and rename them?

What I'm looking for is doing the same thing selecting the source image in the Inspector does, except with code.