How to upload new version of a document?

The following link has the steps below for uploading a new version of a document. However, when I click on the action drop down menu there isn't a Revisions option (see screenshot) Does anyone know how to complete this step?

http://www.zoho.com/online-document-management/zoho-docs-faq.html#tab3

How to upload new version of a document?

Its easy to upload document with revised versions.
To upload new version of a document

Select the file for document revision.
Click on 'Actions' button on the toolbar and select 'Revisions' option from the drop-down menu.
A dialog box appears with document version details and upload form.
Click on browse and select the new version of files from your local drive.
Click on "upload" to update the new version.

For more details refer: Document Revisions.