They can be impeached similar to any other high ranking official. Essentially, the House can impeach them, the Senate can vote to remove or acquit them. I don’t think it has ever happened though.
In practice, there is next to zero chance of them being removed that way. Take Thomas for example, the most insane SCOTUS on recent history. Even if Dems control the House and have 60 votes on the Senate, impeaching him will likely be highly unpopular. I mean, impeach him for having different political beliefs to you is hardly a just reason to get impeached.