In CentOS with PHP-FPM and Nginx, to change file-size limit, the configuration differ slightly from which in Ubuntu with mod PHP for Apache (libapache2-mod-php5/php5) and Apache.
Same configuration
Add this line to wp-config.php
define('WP_MEMORY_LIMIT', '256M');
Different configuration:
For Apache + mod PHP
For Nginx + PHP-FPM
Edit virtual host file of nginx, within tag server, add in
client_max_body_size 256M;
Find php.ini file
locate php.ini
And edit/add these lines
post_max_size = 256M
upload_max_filesize = 256M