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Why is my zipfile filesize limited?
This is done by the host of the webserver in the php.ini file. If you are on a shared host, and you can't get to the php.ini file you can choose to enter the following into you .htaccess file in the root of you Joomla! install in order to bypass this restriction.
<IfModule mod_php4.c>
php_value upload_max_filesize 10M
</IfModule>
If the server has the module mod_php4.c installed, the maximum upload value will now be 10MB.