You can upgrade your mysql version from 5.0 to 5.5 by using following steps
1. Enable remi repository for yum
wget http://dl.fedoraproject.org/pub/epel/5/i386/epel-release-5-4.noarch.rpm
wget http://rpms.famillecollet.com/enterprise/remi-release-5.rpm
sudo rpm -Uvh remi-release-5*.rpm epel-release-5*.rpm
2. Run mysqldump to export data out from MySQL 5.0
mysqldump -uroot -p –all-databases > mysqlbackup.sql
3. Run ‘yum –enablerepo=remi install mysql mysql-server mysqlclient’
4. Run mysql_upgrade (part of mysql-server.rpm) to clean up the upgraded package
mysql_upgrade -u root -p
5. Adjust my.cnf (version 5.0) for version 5.5
6. Restart MySQL if needed
