Help with App.previousinstance

O.K. In my program what I want to do is when it is run to check if a previous instance of the app is running and if it is to kill the previous instance and then if possable to also delete the file of the previous on. The idea behind this is to make it easy to auto-update.

If I go like this:
if app.previousinstance = true then end

It will end the current app. Which is how it should work. Just wondering if any one could give some some code here and point me to a web page on this. Thank you.