if you have an upload limit for your site or you need to upload a larg sql file with phpmyadmin or you want to upload larg images you can extend it with this command. Just add it to your .htaccess file.

php_value upload_max_filesize 42M 
php_value post_max_size 42M

or keep it permanent and add it to your php.ini by edit the followings:

memory_limit = 42M
upload_max_filesize = 24M
post_max_size = 42M