By default, Drupal enforces file-size limits on uploads. Although there is a place in Drupal's File Upload settings to alter the maximum file sizes (/admin/settings/uploads), chances are your PHP settings limit file size to 2MB or so.

However it's easy to change. Simply upload a file called php.ini containing this line to the directory containing drupal :

memory_limit = 50M

upload_max_filesize = 10M 

post_max_size = 20M 

This will raise the available limit, and you can then change the settings for each Drupal role on the settings page within Drupal:

http://yourdrupalserver.com/admin/settings/uploads