Ask HN: How do you transition your projects to use newer technology?

I've worked at a number of startups and usually, once the technology is picked for the initial stage project, it takes a monumental effort to ever upgrade it. Obviously, there is no reason to upgrade to the "next hot thing"; however, there are lots of situations where it seems like the way to do it.

For instance, moving from Angular 1 to Angular 2 or React. Using libraries like Redux to deal with data flow. Or using TypeScript for type safety.

Even larger jumps are moving from one language or platform to another.