due to my ignorance and the need to use a programm I can't install on Ubuntu 12.10, I decided to uninstall it to install Ubuntu 12.04 (64 bit, because I have a 64 bit laptop). I have only Ubuntu 12.10 as OS and no idea of the procedure (I can't find it in this forum or on the site, there are only instructions useful if you have also Windows or other softwar running with Ubuntu, which I have not.) I can't even download Ubuntu 12.04 on my usb pen drive, because it stops at some point. It says that usb-creator-gtk crashes with SIGSEGV at the executable path /usr/bins/usb-creator-gtk. Any Idea? Thanks in advance for you help!
There isn't a way to revert to an older version of Ubuntu once a newer version is installed, so if you want to go from 12.10 to 12.04, you will have to download and install 12.04 or earlier. As to why you are unable to download it, that should probably be another thread. Edit: More details on downgrading: How to roll back Ubuntu to a previous version?