http://phab.example.com/config/edit/storage.upload-size-limit/?issue=config.storage.upload-size-limit
Should have a link pointing to the article, right now it just mentions it should be looked at.
To configure file upload limits, consult the article 'Configuring File Upload Limits' in the documentation.
https://secure.phabricator.com/book/phabricator/article/configuring_file_upload_limits/