customize a font

I need help to modify a font. In fact I can create the modification I need myself, in a vector graphics program if the designer can just deliver all of the relevant characters to me in vector format, then create the new font with my modified characters. So in other words, I need: 1. All the characters (glyphs?), from a specific font, delivered to me in vector format. 2. My modified characters added to the new custom font.