By default Ubuntu check for updates daily. If for any reasons you want to change the schedule so that Ubuntu check for updates once in week or month or never, here is how to that:

• Open Update Manger (by typing Update in Unity Dash)
• In Update Manger click on Settings
• In there go to Updates tab and change the schedule to available options like: every two day, once a week, every two week or never
• Close it

Question and suggestions are welcomed. Cheers