I think it's easier to disable the constraints, do whatever you want and then reenable them again, this is better then dropping all the schema,....
if you want to remove a solumn from a table do the following :
1- create a new table without constraints, and without the filed you want to remove.
2- do the following insert :
insert into new_table select field1,field2,,,,, from old_table
3- drop table old_table;
4- rename new_table to original_name;
5- create constraints and triggers on the table.

lengthy procedure but, it's the only one available to delete a column.

SURPRISE :
if you want to rename a column, there is one way to do it. I don't suggest that you do it on a production environment, do it only on development environment, I think that after going production you don't need to rename columns.
the procedure is :

select object_id
into MY_OBJ_NUMBER
from dba_objects
where object_type='TABLE'
and object_name='MY_TABLE'
and owner='ME'

select col#
MY_COL_NUMBER
from col$
where obj#=MY_OBJ_NUMBER
and name='OLD_NAME'

update col$
set name='NEW_NAME'
where col#=MY_COL_NUMBER
and obj# = MY_OBJ_NUMBER

do you beleive it ?
I didn't beleive until I tested it.