Centos – Upgrade thesql version

I am trying to upgrade mysql package to 5.5 on centos. (amazon image – ami-cc5af9a5)

There is 5.1 version of mysql-libs that can not be uninstalled because postfix is dependent upon it. But I can not upgrade to 5.5 version unless I uninstall this 5.1 lib version of mysql.

# rpm -qa  | grep -i mysql
mysql-libs-5.1.61-4.el6.x86_64

# rpm -e mysql-libs-5.1.61-4.el6.x86_64
error: Failed dependencies:
    libmysqlclient.so.16()(64bit) is needed by (installed) postfix-2:2.6.6-2.2.el6_1.x86_64
    libmysqlclient.so.16(libmysqlclient_16)(64bit) is needed by (installed) postfix-2:2.6.6-2.2.el6_1.x86_64
    mysql-libs is needed by (installed) postfix-2:2.6.6-2.2.el6_1.x86_64

Can someone let me know how to uprade to MySQL 5.5 without affecting the other packages?
I have downloaded rpm's because yum install / upgrade does not work since it has 5.1 version built-in.