Prompt for new Version of Database forms

I have database forms on 68 different computers. I send them an update periodically as the database changes. How can I make it so that if they have an old version of the forms that when they open the database it prompts them that they have an outdated version and then when they click ok it takes them out of Access. This way I can stop tracking when they have completed the task because they won’t be able to use the older version.