Profile Settings: Visit the profile page of the person from whom you want to stop receiving notifications. You can find their profile page by going to your "My Contacts" page and clicking on the profile. Once on the profile page, there is bell icon that allows you to manage notifications from that specific person. You can click to enable, or disable notifications anytime from that person to adjust.
Account Settings: In your account settings, look for a "notifications" tab. There you find and to customize what types of notifications you receive and from whom. Click on the "Manage" button for Individual Contacts.
Unfollow: Altermatively, If you don't want to receive any notifications at all from a specific person, you could consider unfollowing them.