I'm getting a warning on a project in the IDE:

"Project was created in an older version of the Force.com IDE and must be upgraded to be used with Winter '11.  You will not be able to save or refresh files in this project from the server until you upgrade it.  To upgrade, use the upgrade wizard by right-clicking on the project in Package Explorer and choosing Force.com > Upgrade Project. " 

1) I've update Eclipse(helios)  to latest Force.com IDE release

2) Right clicking on project does NOT give an option to "upgrade project"

3) Despite the warning,  i am able to save and refresh files from the server

4) I've tried closing project, restarting eclipse and then re-opening project.

How do i upgrade this project?

Peter