I have a pc with windows 7 and Ubuntu 12.10 dual boot. I want to remove Ubuntu 12.10 and I want to install Ubuntu 10.04LTS because my Micromax Wireless 3G modem is not supported in Ubuntu 12.10. Can you please tell me how can I do that?
The simplest procedure would be to boot with the Live CD for 10.04LTS.
Install it on the current / partition by formatting it during installation. Select other partitions like home, swap etc. if applicable but do not format them.
When you reboot, Grub menu should indicate Ubuntu 10.04 LTS.