I dual booted windows 7 with windows xp and deleted the iso file which i downloaded from microsoft. Tell me how to uninstall windows 7 without affecting xp and changes which i should make in c drive in which xp i already installed.
Either way, you could format whichever drive/partition it is on with a partition manager like EASEUS. Then you could just edit out the W7 boot entry by running 'msconfig', or use your XP disc to go to the recovery console and use the 'fixboot' and 'fixmbr' commands to write a new boot sector/mbr.
This will wipe W7 and also it's boot entry. Good luck!