Update function for my Software (running as a service).

I have a program that is running as a service installed by NSIS and need a update function for this. I need a timer/buckle that connect to my server each X minutes for know if the software must be updated. The server will answer with a json with a MD5 hash and an URL. The md5 hash is the hash of new software file, then our current software need check if the hash of current software is different to hash that server did answer us, if is different then download the new software file that server answer us in URL. Once downloaded URL (new version of our program) we need recheck if md5 of downloaded file is equal to hash that server gave us (this is for check if new software was downloaded correctly) Then proceed to Updated. exit of current and start the new version. remember that my software is running as a services. we need found the better way for made the update optimized for not fails. I think the new software will must be made in NSIS that install as a services like the current software, then when downloaded the new install it and remove old itselt. I attached an example