Uninstall mysql on Red Hat Enterprise Linux

List currently installed packages..
#rpm -qa | grep -i '^mysql-'

Then remove one-by-one

rpm --nodeps -ev MySQL-first-package
rpm --nodeps -ev MySQL-second-package

rpm --nodeps -ev MySQL-last-package

Once you remove all packages you download all MySQL 5.4.* packages into a dir and run below command

rpm -ivh MySQL-*.rpm