删除自带yum：rpm -aq|grep yum|xargs rpm -e --nodeps
下载安装包：
#wget mirror.centos.org/centos/6.4/os/x86_64/Packages/yum-3.2.29-40.el6.centos.noarch.rpm
#wget mirror.centos.org/centos/6.4/os/x86_64/Packages/yum-plugin-fastestmirror-1.1.30-14.el6.noarch.rpm
#wget mirror.centos.org/centos/6.4/os/x86_64/Packages/yum-metadata-parser-1.1.2-16.el6.x86_64.rpm
安装
#rpm -ivh yum-3.2.29-40.el6.centos.noarch.rpm
#rpm -ivh yum-plugin-fastestmirror-1.1.30-14.el6.noarch.rpm yum-metadata-parser-1.1.2-16.el6.x86_64.rpm
在线升级
#yum check-update
#yum update
#yum clean all