Any Idea?

i want to ask about something…
i made a software using php , ajax and javscript…

now as any product i want to make updates on my software, when any updates is available, i want to let the user knows that there is a new update with a new version so the user can download it…

Example: like the update of mccafe, windows…etc…

my idea is to use the webservice and let the software when loggin-in uses the webservice to check if there is any updates and tell the user with a message the version is updated,please download new version

but till now i can not make this webservice…

Any idea of using webservice or any other idea???