The details of theme bundled icons :-
http://support.livemeshthemes.com/faqs/how-to-use-1500-icons-bundled-with-the-agile-theme/
You can build your own icon lib at IcoMoon and do it but you will need to look in the theme code and sample data to ensure that existing icons are replaced with the right icons that are made available with the new icon fonts generated. Will be couple of hours of work and when you want to update the theme, you will have to be careful unless you manage to make all changes in the child theme.
Unless you have a large number of custom icons to handle, my recommendation would be to use the icommoon app to choose the exact icons you need and use the PNGs generated (basically use it as an image). You can override size, color etc. of the icons generated in the icomoon app settings.
File structure : images/icons/icomoon