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:
less /usr/share/doc//changelog.Debian.gz
Notes:

• 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/–/ChangeLog.gz but it may be the upstream source that does not include any after-the-fact patches.