Updating client table definitions from server tables without losing client data

Hi...

I want to create an automatic update application. In this application, I need to update the database because new versions of a program may use newly created tables or modified tables, if compared to the older version program.

So, I have a database version 2.0 in Computer 'A', and I need to make a script that I can run in Computer 'B' (still running version 1.0 of the database). After the execution of the script, Computer 'B' tables should be exactly the same as Computer 'A' tables.

But no data should be involved in this, all data in Computer 'B' should be kept, and no data from Computer 'A' should be transferred to Computer 'B'.

I tried to use pg_dump (in 'A') and pg_restore (in 'B'). I only have success with pg_restore with the --clean option, but it erases all data.

Can anyone help me on this?
Thanks!
(sorry the not so good english ;) )