Updates/Changes to a database

I am building an application with Postrges as the backend foundation.
This is my first application and it has struck me that as we add
features/functionality to the application and database with each new
version, we will need some method of obtaining the current structure
of the customers database and then modifying/updating the structure so
that it matches the application revision standard.

Are there pre-existing tools out there that does this sort of thing ??

My present direction is to create a small SQLite db that has there
expected structure, compare each table against the SQL
"information_Schema.columns" and the create a series of SQL commands
to be executed that would add columns and/or table as needed.

-- any thoughts or comments ?