[Koha] i need your help on installing koha

hi guys, i am trying to install koha on a debian pc and when i run apt get update i get the following error messages Err http://ftp.indexdata.dk indexdata/sarge/released Sources 404 Not Found Err http://ftp.indexdata.dk indexdata/sarge/released i386 Packages 404 Not Found Fetched 197 B in 18s (11 B/s) W: Failed to fetch http://ftp.indexdata.dk/debian/dists/indexdata/sarge/released/source/Sources... 404 Not Found W: Failed to fetch http://ftp.indexdata.dk/debian/dists/indexdata/sarge/released/binary-i386/Pa... 404 Not Found E: Some index files failed to download, they have been ignored, or old ones used instead. your help will be highly appreciated.