Create a test.php with the following content to check your current maximum
upload size.
<?php phpinfo(); ?>
Search your php.ini in the Apache folder:
$ find /etc -name 'php.ini'
/etc/php5/cli/php.ini
/etc/php5/apache2/php.ini
Edit it. Set upload_max_filesize and post_max_size to whatever you want.
Restart the server with
$ sudo service apache2 restart