如何使用按钮调用数组中的下一个和上一个值？

I want the "displayround" div to show a certain value in my array. When the page loads the first value in the array (1/38) is being displayed. When I press the "next" button I want it to show the next value in the array (2/38) and so on. And when I press "previous" button I want it to display the value that comes before the displayed value. I want the "displayround" div to show a certain