SQL SERVER Enterprise Question from a rookie!

Our company continuiously needs to Update the Databases that are on our
client's systems since with have newer version every couple of months, but
the main problem is that each time we update it, we need to erase all the
data that was already put in by the client...I am sure there is a way to
backup the data of the tables somewhere and update the database changes
and then "reload" the old data into the new database.... This is needed
for both the customers data and some of the system's data.
HELP! I am a rookie in a need of an EXPERT!!
Take CARE!!
Sarah Illouz
Concordia University

Process or procedure changes depending on the type of change.

DTS or OSQL or BCP or simple scripts are used inorder to do this.