To find the change log for a package on RPM (Redhat, Fedora Core, CentOS, SUSE) based systems:
rpm -q --changelog package | more
To find it on Debian / Ubuntu systems:
- files above a certain size are automatically compressed
- there may be other changelogs in there as well (for the upstream package)
RPMs typically have /usr/share/doc/<packagename><version> /ChangeLog.gz but it may be the upstream source that does not include any after-the-fact patches.