Deletion of sessions

Hi all,

I am new to RoR, I want to delete sessions, and dont know how and where to use the following,

ActiveRecord::SessionStore.Session.delete_all ['updated_at < ?', 1.week.ago] or ActiveRecord::SessionStore.delete_all ['updated_at < ?', 24.hours.ago]

In environment.rb, I have   config.action_controller.session_store = :active_record_store

Please help me, its urgent