In the iOS app you can change your notification settings by opening your profile page, clicking on settings, and opening the email notification or push notifications pages. There you can manage your notifications to set which notifications you would like to receive.
On the desktop website, after you log in there is a white arrow in the upper right next to your profile picture. Clicking on that will open a drop down, select Notification Settings. This will open a page that will allow you to turn all of your notifications on or off.