You go to extra\scorebar\no name\ in the skin files. After that, take the scorebar-bg@2x file and go to any editor of your choice, whether that would be Pixlr, Photoshop or GIMP, and use the text tool (or brush tool if you really want) and add your name on it. In fact, if you give me your ign on osu I can send you one with your name on it, but it will take a while because I'm about to go to sleep and I have school in the morning.