How to update the html5 appcache files only when the user want to update

I am working on a offline Html5 web application. In this i use the HTML5 APPCACHE for offline purpose. I want to handle this cache functionality on user will. Means whenever a user visit this web application he will get the promt msg to change version if he choose to no then this application should work on old version of appcache (* After refreshing or reloading this web page should work on old version) Now if user choose yes the his application must use the new version.........


Please if anyone can help me please do it i need it seriously....

Thanks.