Enfold – Fontello, can I just upload a single icon?

I need a icon to be added to the default icons of the site.
I downloaded it from the fontello site but before I press upload on the admin panel I want to make sure it does not remove the current default fonts and just adds to the available ones?

Let me know if that is what is does or do I need to download a full set that has all the icons I may be using in the theme already i.e it is not possible to just add one or two icon but you need to replace all of them

EDIT: Or do I need to export the current json of the them to the fontello site and then add the icon I want then download the new archive?