How change font of body and header?

The theme is not designed to color customization via theme settings. This can be done only via CSS. To set your font styles, add this CSS Appearance menu→ Customize → in  Additional styles:

/* body font settings */
body { 
   font-family: Arial, "Helvetica Neue", Helvetica, sans-serif; /* family */
   font-size: 18px;   /* font size in pixels */
   line-height: 125%; /* line height in percents */
   color: #0085ff;    /* text color */
}

/* H1 font settings */
h1 { 
 font-family: Arial, "Helvetica Neue", Helvetica, sans-serif; /* family */
 font-size: 48px;   /* font size in pixels */
 line-height: 125%; /* line height in percents */
 color: #0085ff;    /* text color */
}

/* H2 font settings */
h2 { 
 font-family: Arial, "Helvetica Neue", Helvetica, sans-serif; /* family */
 font-size: 36px;   /* font size in pixels */
 line-height: 125%; /* line height in percents */
 color: #0085ff;    /* text color */
}

/* H3 font settings */
h3 { 
 font-family: Arial, "Helvetica Neue", Helvetica, sans-serif; /* family  */
 font-size: 24px;   /* font size in pixels */
 line-height: 125%; /* line height in percents */
 color: #0085ff;    /* text color */
}
/* H4 font settings */
h4 { 
 font-family: Arial, "Helvetica Neue", Helvetica, sans-serif; /* family */
 font-size: 20px;   /* font size in pixels */
 line-height: 125%; /* line height in percents */
 color: #0085ff;    /* text color */
}

Value for font family you can get fron web-safe fonts list. Hex color code find here.