class ActiveRecord::ConnectionAdapters::Table

def change(column_name, type, options = {})

t.change(:description, :text)
t.change(:name, :string, :limit => 80)
===== Examples
See TableDefinition#column for details of the options you can use.
Changes the column's definition according to the new options. 
def change(column_name, type, options = {})
  @base.change_column(@table_name, column_name, type, options)
end