Hi Ellen,
Please use the following css to increase the size of logo:
.sleeky-logo-placeholder img {
width: 55%;
height: 0%;
}
And you can use the following css to change the font size for the menu:
.navmenu > ul > li, ul.navmenu > li a {
font-size: 20px;
}
NOTE: Please use the child theme style.css or custom css plugin to write the css.
Thanks