This post is older than a year. Consider some information might not be accurate anymore.
The file upload size is set in your PHP configuration, php.ini, with the parameter
upload_max_filesize. You may change it, if you run e.g. a private wiki (MediaWiki, DokuWiki) or an CMS like WordPress.
Example for Debian
Change from 2M to 10M
; Maximum allowed size for uploaded files. upload_max_filesize = 10M
You need to reload your apache configuration before you can upload the file.
service apache2 reload