Are you using an FTP program to access that location? If not, you need one, such as the popular Filezilla, which is free.
But if you are using an FTP program and access where your WordPress site files are, then you need to go into:
your site files here >> wp-content >> plugins >> layerslider >> static >> skins
Also, we are talking about the LayerSlider plugin and not the Widgetkit one right?