To install APC follow the below instructions:
First, log in to the server as a root
Download APC

 

# wget http://pecl.php.net/get/APC-3.1.3p1.tgz

 

Extract and move into the directory

 

# tar xfz APC-3.1.3p1.tgz

 

# cd APC-3.1.3p1

 

Install some required dependencies:

 

# yum install php-devel pcre pcre-devel

 

Compile APC using:

 

# phpize

 

# ./configure

 

then run the following commands:

 

# make

 

# make install

 

Edit php.ini in regular way, add:

 

[APC] extension=apc.so
apc.apc.stat = 0
;apc.include_once_override = 1
apc.shm_size = 64

 

Restart apache. To check if APC is installed you may copy apc.php from same source directory to domain web accessible folder.
Open domain.com/apc.php in browser . On that page you should see more Hits than Misses ( >90% is great result)

How To install APC