downgrading

do you have anything else installed on the system? do you have all your files backed up?
if so when you are installing from the cd choose to use entire hard drive option. that should work fine
WARNING!! all data will be GONE off your hard drive when choosing this option... make sure you have everything backed up that you want to keep..

No ubuntu is the only os i have.Yes everything is backed up!
but i already used the entire hard drive what should i do then?
when i try to preinstal it shows that there are no partitions that i can choose...

Are you using the normal 8.04 CD to install? Then there should be an option to use the entire disk, when you start installing. If you're using another CD, then please explain.

Yes i have a cd but its 7.04 version!Maybe thats why it doesnt install...

OK, so can you download/acquire the 8.04 version then? Or do you want to downgrade to 7.04?

i want to downgrade to 7.04 tho beacause i started form it and evntualy upgraded it
but if i have no other options i can try to download 8.04 only i need a bit explanation how to do it

OK, I see. To confirm, do you have all your data backed up? (You can confirm and are 110% sure that you wont lose data if I give you instructions to nuke your partition table so that when you boot/install from your 7.04 CD it will see just an empty disk?)

yes i just did back up everything...
okay you can give the instructions

OK. Boot from your 7.04 livecd, then open a terminal. (should be "Applications" menu -> "Accessories" -> "Terminal"

At the prompt, type the following line and press enter after typing it:

cat /proc/partitions

You should get some output, similar to this:

major minor #blocks name

   8 0 312571224 sda
   8 1 306528201 sda1
   8 2 1 sda2
   8 5 6040408 sda5

The bit we're interested in is the bit at the end of the second data line, e.g. in my example it's "sda". This is the name of your hard disk device. It will probably also be "sda" for you, but it *may* be "hda" or possibly something else.

Next, type at the prompt type the following (and press enter after typing it):

sudo dd if=/dev/zero of=/dev/sda bs=512 count=1

Where the command above shows "sda", you should substitute whever you found your disk identier to be from the previous command. The output should be something like:

1+0 records in
1+0 records out
512 bytes (512 B) copied, 4.5227e-05 seconds, 11.3 MB/s

If you've had success so far, then reboot your PC and restart again with the 7.04 CD. You should find that your disk now appears unformatted/empty and you should be able to install without trouble.

ok this solved my problem but my friend has the same problem only he has the8.10 but he wants to downgrade too only he has the 7.10 live cd.
does he has to do the same routine?or something diffrent

Same routine would work. At the risk of repeating the obvious, he should make sure everything is backed up before going through the process.