How to change gallery shortcode column number

As default gallery shortcode has a 2 column layout;

Screenshot_2

If you want to change it;

Go to Appearance->Theme Settings->General and copy paste the following code to the custom header script field;

<style>
.da-thumbs li {
    width:25% !important;
}
</style>

After this change, your galleries will look like this;

Screenshot_1

If you want to make it three column, you can change width value with 33.333333 like on the following example;

<style>
.da-thumbs li {
    width:33.333333% !important;
}
</style>

If you want to make it one column, you can change it with 100% .