Making of the Tentacle upgrade script
The best scenario for keeping Tentacle up to date is using to use Git.
If for some reason you can not use git then for the majority of users we have you covered.
Tentacle updates are powered by the Serpent API. Serpent is designed to allow developers to continue their normal workflow and control when Updates are made available.
By creating a version git tag I can publish an archive file that is ready for public use.
Tentacle will have a look at its own internal version and compare it with what is available over the API at http://api.tentaclecms.com/get/core/