Download Zend Optimizer from the command line of the server.

wget http://downloadspot.com/downloads/ZendOptimizer-3.3.9-linux-glibc23-i386.tar.gz

Then untar

tar xvfz ZendOptimizer-3.3.9-linux-glibc23-i386.tar.gz

Then enter the Zend directory

cd ZendOptimizer-3.3.9-linux-glibc23-i386/data/

Then find the phpversion match .so file

Copy the full patch to the file:

zend_extension=</root/ZendOptimizer-3.3.9-linux-glibc23-i386/data/5_2_x_comp/ZendOptimizer.so>

Then copy the full path to the file php.ini file located in the /usr/local/lib/ folder:

zend_extension=</root/ZendOptimizer-3.3.9-linux-glibc23-i386/data/5_2_x_comp/ZendOptimizer.so>

Restart Apache

Or if you luck enough to have CPanel installed for example with a hosting account from DWHS then just login as root and run:

/scripts/installzendopt