The syntax of dropping a column is pretty easy.
SQL> show user
USER is "HR"
SQL> alter table employees drop column salary;
Table altered.
As long as there's no referential constraint on it.
SQL> alter table employees drop column employee_id;
alter table employees drop column employee_id
*
ERROR at line 1:
ORA-12992: cannot drop parent key column
Now you have to deal with ORA-12992 first.