How to remove the blogger header

Just enter the shown code below on your template XML after the </body> and before the </html>:

</body>
<script>
var a = ["b-navbar", "header"]

for (var i=0; i < a.length; i++) {
var ai = document.getElementById(a[i])
ai.style.visibility="hidden"
ai.style.display="none"
}
</script>
</html>