To increase max upload size you can use following methods

php.ini

1) You can use the .htaccess file to increase the file upload size of the server.
Add below codes in the server .htaccess file of the site

php_value upload_max_filesize 128M
php_value post_max_size 128M
php_value max_execution_time 300
php_value max_input_time 300


2)if htaccess trick does't  work you edit the php.ini file of the server. 
To increase the file upload size please add following codes in a file named "php.ini" and upload to the server

upload_max_filesize = 64M   
post_max_size = 64M
max_execution_time = 300

3)you can use the wordpress config.php file to increase the wordpress file upload limit. Add below code snippets in config.php

define('WP_MEMORY_LIMIT', '128M');


4) You can also use the theme functions.php to increase the file upload size. The code will set the the upload settings as per the code

@ini_set( 'upload_max_size' , '64M' );
@ini_set( 'post_max_size', '64M');
@ini_set( 'max_execution_time', '300' );