I tried to update MySQL from 5.1 to 5.5 in CentOS 6.2. The following is the process I did:
1. rpm -Uvh http://repo.webtatic.com/yum/centos/5/latest.rpm
2. yu
yum list installed | grep -i mysql
yum remove mysql mysql-*
rpm -Uvh http://dl.fedoraproject.org/pub/epel/6/i386/epel-release-6-8.noarch.rpm
rpm -Uvh http://rpms.famillecollet.com/enterprise/remi-release-6.rpm
yum --enablerepo=remi,remi-test install mysql mysql-server
yum list installed | grep -i mysql
/etc/init.d/mysqld start ## use restart after update
service mysqld start ## use restart after update
chkconfig --levels 235 mysqld on
mysql_upgrade -u root -p
Now my MySql version is 5.5.32
http://www.webtatic.com/packages/mysql55/
http://www.if-not-true-then-false.com/2010/install-mysql-on-fedora-centos-red-hat-rhel/
Hope it help some one
NOTE: Adding comments from @pim (in comments)
Just wanted to add that after the upgrade, my crontab was removed as well. Had to reinstall with "yum install vixie-cron" (CentOS 6)