Margin on Caption/img

Use CSS via ‘additional CSS’, not in the editor.

These are the defaults for your theme

.wp-caption.alignright {
    margin-left: 20px;
    margin-right: 0px;
}

and

p.wp-caption-text {
    padding: 10px 0px;
    text-align: center;
    margin-bottom: 0px;
}

To add CSS: use the “Additional CSS” option in the customizer. https://codex.wordpress.org/CSS#Custom_CSS_in_WordPress

Learn to use the Chrome Developer Tools to help you see and test changes to your CSS.