You are missing /wp-content/themes/YOUR_theme_NAME_FOLDER
like this:
function sliderimgchange(){
if ($(window).width() <= 600) {
var sliderOne = $('.slideuno').attr('src', '/wp-content/themes/YOUR_theme_NAME_FOLDER/images/sliderone-mobile.jpg'),
sliderTwo = $('.slidedos').attr('src', '/wp-content/themes/YOUR_theme_NAME_FOLDER/images/slidertwo-mobile.jpg'),
sliderThree = $('.slidetres').attr('src', '/wp-content/themes/YOUR_theme_NAME_FOLDER/images/sliderthree-mobile.jpg');
} else if ($(window).width() > 600) {
var sliderOne = $('.slideuno').attr('src', '/wp-content/themes/YOUR_theme_NAME_FOLDER/images/sliderone.jpg'),
sliderTwo = $('.slidedos').attr('src', '/wp-content/themes/YOUR_theme_NAME_FOLDER/images/slidertwo.jpg'),
sliderThree = $('.slidetres').attr('src', '/wp-content/themes/YOUR_theme_NAME_FOLDER/images/sliderthree.jpg');
}
}