How to increase WordPress Upload File size limit

The easiest way is to add the following code into your theme function.php file.
add the following lines

@ini_set(‘upload_max_size’,’128M’);
@ini_set(‘post_max_size’,’128M’);
@ini_set(‘max_execution_time’,’300′);

If your hosting allow, you can edit the php.ini file
add the following lines

upload_max_filesize=128M
post_max_size=128M
max_execution_time=300

Or editing the .htaccess file on your hosting root directory
add the following lines

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

Or you can try this plugin – Increase Max Upload Filesize