Updating database structure

I have a problem with finding a way to update a database structure.
This might be a very simple problem, just cannot find the info.

I am looking at updating the structure of my database. I put an
application on my production server some time ago and further developed
the application till a point I have to merge the changes.

How can I update the structure on the production server to reflect the
database on my test machine in an easy way with preservation of the data
on the production server. There are no major changes in the fields types
etc., mainly additions/deletions of fields in the tables.

Thanks,

Luuk