Re-topology is what that is called.
Here’s a ‘must watch’: https://cgcookie.com/courses/introduction-to-retopology
It’s mostly a manual process, some people love it and some hate it.
There are Addons (like Retopoflow), that can help speedup the process and there are also ones that sort of automate it (haven’t used them). But the first thing is, to learn how to do it by hand.
