LG Lotus

OK, just got the new red Lotus for my wife. With the songs I download from sprints music store, I can assign them to a contact as a ring tone, no problem. But when I hooked up the phone via usb to her pc, It easily copied songs from her pc to the LG Lotus music folder. Then I unhooked the usb cable, found the songs by looking at the memory card manager, then copied them into the music player. So they play, but I can't seem to assign them to contacts. I see an option for "assigned media" but I don't see that mentioned in the manual at all.
How can I get an mp3 that's in the music player assigned to a contact as a ring tone? Please, I need very specific direction. I can follow directions, but they need to be in order and clear please. I've already spent hours dinking around and having read the manual, I'm not sure what to do.