This option will be active only when you already published online the prototype. Once you select the option you will see the following dialog:
Optionally, enter a brief description of what has changed from the last time you published the prototype. This message is only informative for the reviewers and it will be overwritten the next time you 'Reshare' or 'Replace' a published prototype.
If you want the reviewers to be notified via email about this version click the check box.
Once you click the 'Replace' button, the prototype published in your Justinmind account will be replaced with the version you have in your workspace.