How to save the base if you need to change the structure of the Rails project?

Question

Ruby on Rails

What I mean.
For example, I have a working application with an already developed database.
During the update of the application, the database has undergone dramatic changes. (New table links, etc.)
How do you do it in such a case to save the previously accumulated information without harm to users?
PS I am aware that the question may sound silly. But there is no one to ask such questions.

Answer 1

Usually in such cases, they also work to change the user information (usually put in the right columns of the right tables) so that the application continues to function correctly. The best way to do this is to take the base from production and do all the actions on it in the development environment. Well, then to update the production.