Login the server SSH using root

Inorder to check if mysql is already installed or not run this command
which mysql
If found it will show some directory name otherwise not found

In order to remove old mysql
yum remove mysql-server
yum remove mysql

Now to install mysql run this command from the shell or a command line access point
yum install mysql-server
yum install mysql
yum install mysql-devel

Inorder to use with php
yum install php-mysql

service mysqld restart

By default mysql has the no passward. To change the password in command shell write the following commands
mysql
mysql> USE mysql;
mysql> UPDATE user SET Password=PASSWORD(‘new-password’) WHERE user=’root’;
mysql> FLUSH PRIVILEGES;