I am using Ubuntu 11.10 and I want to update it via Internet connection but I am not sure if my / partition has enough space.So what is the proper amount of free space required before upgrading to Ubuntu 12.04 from Ubuntu 11.10?
The update should tell you how much space it will need before it goes ahead but an upgrade requires usually at least as much space as all the packages you have already installed take up.
This is because it needs to download all those packages before it can install them. That needs disk space.
If you're particularly worried, removing some of the bigger, non-essential applications that would be upgraded can help. You can reinstall them afterwards when the initial upgrade packages have been removed.