Change to image buttons

[JVSP]

How can I change the "Post Quick Reply" and "Go Advanced" buttons on the bottom quick reply to image buttons?

These two codes

<input type="submit" class="button" value="$vbphrase[post_quick_reply]" accesskey="s" title="(Alt + S)" name="sbutton" tabindex="2" id="qr_submit" onclick="clickedelm = this.value" />

<input type="submit" class="button" value="$vbphrase[go_advanced]" accesskey="x" title="(Alt + X)" name="preview" tabindex="3" id="qr_preview" onclick="clickedelm = this.value" />

Thanks