i’ve had the same problem. if you are running your site on shared server, you might not be able to edit php.ini, so i fixed it by placing .htaccess in the /wordpress.
here is the code.
#Change upload limits
php_value memory_limit 34M
php_value post_max_size 33M
php_value upload_max_filesize 32M
php_value max_execution_time 600
#Change upload limits end
it does not work always, but worth giving it a try, i think.