Hi @twewscd,

Use the CSS code below: 

#wpdcom .wpd-comment .wpd-avatar img, #wpdcom .wpd-comment .wpd-avatar img.avatar{
    width: 56px !important;
    height: 56px !important;
}
#wpdcom .wpd-comment.wpd-reply .wpd-avatar img, #wpdcom .wpd-comment.wpd-reply .wpd-avatar img.avatar{
    width: 48px !important;
    height: 48px !important;
}

Put the code in the "Custom CSS code" textarea, located in the Dashboard > wpDiscuz > Settings > Styles & Colors admin page.

Don't forget to delete the caches before checking.