Change tagline/menu bar font size?

Firebug https://getfirebug.com/ – try and work with this tool (or a similar tool) to identify the styles of the tagline and menu; then edit the values in style.css of your theme.

.sideHead {
	float:right;
	width:530px;
	margin-top:20px;
	color:#137fcc;
}

you need to add a line with font-size

the menu bar

where?
sidebar:

.sidebar ul {
		padding:0 0 5px;
		font:11px/12px Arial, Helvetica, sans-serif;
	}

footer:

.footNav {
	float:right;
	margin:0;
}

you need to add a line with font-size
or under
.footNav li { ......

https://www.w3schools.com/css/css_font.asp