The following example demonstrates how it could be done.
alter table schema1.my_table drop column unused_field;
There is also an alternative syntax that could be used to drop multiple fields at once.
alter table schema1.my_table drop (unused_field); -- Dropping one field only alter table schema1.my_table drop (unused_field1, unused_field2); -- Dropping two fields
In the second example, if you need to drop more than two fields, just keep adding them within the parenthesis, separated by commas.