We are building an application on the force.com platofrm where we have created a lrge number of custom objects.

We are working on creating user documentation (help and training documents)  and would like to override the default link of Help on the top right corner of the page. 

Please advise how we can override that. If that is not possible, how can i remove that link. I do not want my users to see the salesforce help as that is not relevant to our app.