How to change the text
Get into Admin Panel > Appearance > Redart Options > General > General > Loader Animation > YES > Save All.
Under the Loader Animation option you can enter the loader animation text.
How to change the loader image
Get into Admin Panel > Appearance > Redart Options > Layout > Custom CSS > Enable Custom CSS > Yes > Pasted the below css code inside the text area > Save All.
background: url(http://wedesignthemes.com/themes/redart/wp-content/themes/redart/images/loader-img.png) no-repeat scroll 100% 100% !important;
You can change the image URL as per your need.