function changeBGImage(){
var backImage = new Array(); 
//Change the next line 2 to however many images you want to choose from
var randNumber = Math.floor(Math.random() * 6);

backImage[0] = "bg_home_1.jpg";
backImage[1] = "bg_home_2.jpg";
backImage[2] = "bg_home_3.jpg";
backImage[3] = "bg_home_4.jpg";
backImage[4] = "bg_home_5.jpg";
backImage[5] = "bg_home_6.jpg";

//Duplicate above and follow the same pattern to add more images

    if (document.body){
        document.body.background = 'imgs/'+backImage[randNumber];
    }
}