Is there any way for me to change the font and its size?
There are build in different font sizes within each theme
header 1
written in the html window like this: <h1> header 1 </h1>
header 2
written in the html window like this: <h2> header 2 </h2>
header 3
written in the html window like this: <h3> header 3 </h3>
header 4
written in the html window like this: <h4> header 4 </h4>
For more changes see