1. Go to the Scheduled Tasks tab in your Control Panel
2. Create a new Scheduled Task and select the Steam Update option
3. Give it a name of your choice, Steam Update
4. Type Weekly(etc)
5. Select the date/hour you want the next check for updates to happen
6. Select Recur Every Week
7. Choose the day of the week
8. Select the Script Parameters tab on top and change it to Update only if a new version is available
9. Save the task

Example Pictures