Hi,
You can try with this tweak:
1) Download the zip file for FontAwesome 5 >> unzip and copy its folder to this directory: root/templates/ja_smashboard/fonts/ http://prntscr.com/i3qgms
2) Now you need to load this font to template, open the file: root/templates/ja_smashboard/etc/assets.xml
Under the < stylesheets> tag, add this line:
<file>fonts/fontawesome-free-5.0.4/web-fonts-with-css/css/fontawesome-all.css</file>
http://prntscr.com/i3qh3i
3) Go to menu item you want to change the FA icons > Link Type tab > Link CSS style and add FA icon you want, for example, I want to use Rocket icon for the Travel menu item, I added like this: http://prntscr.com/i3qhaw
Clear all caches then.
Regards