You can easily change the loader that triggers just after you submit the form by using custom CSS.

Here is the CSS code that will change the loader in a minute. Paste following CSS code in custom CSS option of your theme.

.cp-form-processing-wrap .cp-form-after-submit .smile-absolute-loader .smile-loader {
    display: none;
}
.cp-form-processing-wrap .cp-form-after-submit .smile-absolute-loader {
    background-image: url('http://screenshots.sharkz.in/pratik/2016/04/loading.gif');
    background-size: 160px;
    background-repeat: no-repeat;
    background-position: center;
}

In above code, you just need to replace the background image path ( background-image ) with your loader GIF image path.

You can select your loader from here also: http://preloaders.net/