How to change the structure of tables with pgadmin2?

[NH-Jason]

Hi,
    I'm an in-house VB programmer 
working with VB + Pg. pgAdmin2 is very valuable to me. 
 
    I have to change the tables' 
structures (add / delete column name, indexes; change data type ...) from time 
to time. I understand changing some of the schema thing is impossible with pg, 
so I will copy the SQL defination of the schema offered by pgAdmin2, drop the 
table, change the SQL defination and rebuild it. Everything's fine except all 
the data (mostly testing data) gone. Is there existing pgadmin / plug-in feature 
is able to do the job for me?
 
-Jason