One of the premium features in Cloud9 is the ability to create private projects. However, after upgrading you might want to turn an existing public project into a private one. At the moment, we don't have an easy way to turn public Cloud9 projects into private projects.

You can get around this limitation in two ways:

1) download project, upload folder

• open the public workspace
• menu file -> download project
• save the zip file, extract it to a folder
• create a new private workspace & open it
• right click on root in filetree -> Upload to this folder
• choose folder (chrome only) and select the just-extracted folder
• see it upload and confirm all is well
• delete the public project

note: download project does not include hidden files (local git history), so if you have those, download them separately.

2) by using a code-hosting site like Github or Bitbucket to push/pull your Cloud9 projects. You can do so by following these steps:

1. Create an account in a code-hosting site that supports private repositories (Bitbucket offers free private repos, so that might be your best option.)
2. Link the account at the code-hosting site with your Cloud9 account (see Add-on Services under Your Account in the Dashboard)
3. Push the public Cloud9 project you want to convert to private to the code-hosting site.
4. Go to the Cloud9 Dashboard and do a "clone from url" with the url from the new private repository at the code-hosting site and select "Private to the people I invite". That would create a new private project from the repository you provide in the url. 
5. Delete the old public project in Cloud9.

This article might be helpful (skip steps 1 and 2 if you have already added your Bitbucket account through Add-on Services): 
http://support.cloud9ide.com/entries/20754818-push-your-git-cloud9-project-to-bitbucket