Unable to upgrade from ubuntu 7.10 to ubuntu 8.04

Hi,
At present I am using in Ubuntu 7.10 and i would like to upgrade to Ubuntu
8.04.

So I downloaded Alternate CD iso of Ubuntu 8.04 and then I burned them in
the CD.

After burning the CD, I list the the files as below
----------------------
verman <at> verman-desktop:/media/cdrom$ ls -l
total 174
-r-xr-xr-x 1 root root    942 2008-04-22 11:37 cdromupgrade
dr-xr-xr-x 3 root root   2048 2008-04-22 22:59 dists
dr-xr-xr-x 3 root root   2048 2008-04-22 22:59 doc
dr-xr-xr-x 3 root root   2048 2008-04-22 23:00 install
dr-xr-xr-x 2 root root  12288 2008-04-22 23:00 isolinux
-r--r--r-- 1 root root 151400 2008-04-22 23:00 md5sum.txt
dr-xr-xr-x 2 root root   2048 2008-04-22 22:59 pics
dr-xr-xr-x 4 root root   2048 2008-04-22 22:59 pool
dr-xr-xr-x 2 root root   2048 2008-04-22 22:59 preseed
-r--r--r-- 1 root root    221 2008-04-22 22:59 README.diskdefines
lr-xr-xr-x 1 root root      1 2008-04-22 22:59 ubuntu -> .
----------------------

I found a shell script file cdromupgrade and tried to excute the file and
found errors as below.
----------------------
verman <at> verman-desktop:/media/cdrom$ sudo ./cdromupgrade
tar: ./dists/stable/main/dist-upgrader/binary-all//hardy.tar.gz: Cannot
open: No such file or directory