To change the syntaxhighlighter settings, access the shCore.css from ftp. Change font-size and width from there.
Before
.syntaxhighlighter { width: 100% !important; margin: 1em 0 1em 0 !important; position: relative !important; overflow: auto !important; overflow-y: hidden !important; font-size: 1em !important;
After
.syntaxhighlighter { width: 115% !important; margin: 1em 0 1em 0 !important; position: relative !important; overflow: auto !important; overflow-y: hidden !important; font-size: 12px !important;