Hello,
Please try to add this code in custom.css file.
.blog-post .wp-picture img {
position: relative;
left: 50%;
margin-left: -430px;
}
Here is a video tutorial how to create custom.css: https://www.youtube.com/watch?v=Qok2zRedRMY&feature=youtu.be.
Regards,
Robert Hall.















