To unsubscribe from a thread, users can access their subscribed threads through the quick links and select the desired thread using the checkbox. After selecting, they should scroll down to change the subscription type or remove it entirely. Additionally, users can adjust their email notification settings by clicking on the "My PF" link, then "Edit Options," and selecting "No email notification" in the Default Thread Subscription Mode section. This will prevent any email notifications for threads they participate in. Adjusting these settings effectively reduces unwanted email notifications.