Due to concept of this template, it set the max-width for this view in article page. In order to override this, you can try this custom css rule:
@media (min-width: 992px){
.item-page.layout-default.no-sidebar .bottom-article-info,
.item-page.layout-default.no-sidebar .top-article-info,
.item-page.layout-default.no-sidebar .full-image {
max-width: 100%;
}
.item-page.layout-default.no-sidebar .top-article-info {
text-align: center;
}
}
I added into this file for you: /templates/ja_purity_iv/local/css/custom.css