More often than not, modifying a font is not allowed by the licence (I did not verify this particular one) and the best thing to do is to ask the designer to add the missing characters. If you're given permission to modify it yourself, you will need a font editing/font creation software
First seen on DaFont: June 22, 2013
Nothing much is to be found inside the font file either except that it was made using myscriptfont.com...
My guess is that it really is free but I would definitely try to reach her first: firstname.lastname@example.org
Fuseau horaire : CEST. Il est actuellement 00:23