I want to update kernel at fedora 16 to 17. So I need to delete unused files.
find /etc /var -name '*?.rpm?*'
Is that enough or need more extensions?
What are exactly your "unused files", and why do you want to delete them? If you run out of space in /var, "yum clean all" should get rid of the yum cache (grows quite big). Other files that you can safely delete are /var/log/. (old log files), and you might even delete the /var/log/ files themselves.
When you upgrade, the process will get rid of old versions of what is installed automatically. If space is tight, you might want to look at "yum installed" and get rid of stuff you don't use (be careful, "yum info " or "rpm -qi " tells you what the package is all about; "rpm -q --whatrequires " tells you what is using the package. Reckless "yum erase " will delete the package with whatever depends on it...
Take a look at the documentation for yum and rpm.
The yum-utils package contains package-cleanup, with lots of options for cleanups as discussed above.