I just did, from the SanDisk website:
http://www.sandisk.com/Assets/File/pdf/guides/e200/e200_userguide_en.pdf
This manual works for the e200 series, which includes the e280. It looks like you can delete music directly from the player, as well as by using your computer. But if this doesn't help, I'm sure someone in this forum has one and can help you.
Help! I have the E280 and I have some music on it that I want to delete. However, I cannot figure out how to do this! I tried looking at an owner's manual online but it doesn't have the 280; tried looking at another model but this didn't help. Does anyone know how to do this?? Also, the music that I want to delete does not show up when I connect it to my computer (have tried changing USB modes,too) so I can't do it that way. I hope someone can help because this is just driving me nuts!!!

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic