There are many ways to increase file upload size, but best way is, just create a php.ini file, paste bellow code in php.ini and put it into wp-admin.
upload_max_filesize = 64M post_max_size = 64M max_execution_time = 300
Other way is to change in php.ini, and paste above code, but we are not able to change it by own on server.
One other way is put bellow code in function.php, but some tome it is not work.
@ini_set( ‘upload_max_size’ , ’1024M’ ); @ini_set( ‘post_max_size’, ’1024M’); @ini_set( ‘max_execution_time’, ’1000′ );
We also do it with .htaccess file, just put bellow code in .htaccess file
php_value upload_max_filesize 1024M php_value post_max_size 1024M php_value max_execution_time 1000 php_value max_input_time 1000</pre>