problem upgrading 13.04 to 14.04

[Bernard]

Hi to Everyone,

I have seen docs to either carry a direct upgrade or do it in two steps, 
first 13.04 to 13.10 then 13.10 to 14.04. Problem is: it seems that I 
can't update my /etc/apt/sources.list using the address below, since it 
says it is restricted and that errors have occured:

sudo sed -i -e 
's/archive.ubuntu.com\|security.ubuntu.com/old-releases.ubuntu.com/g' 
/etc/apt/sources.list

Have these archives been moved to another address ?  How should I operate ?

I hope I don't have to re-install a newer ubuntu from scratch, since I 
would then have too many things to re-install.

Thanks in advance for any input

Bernard