You can view any Email Reminders set up against an Activity in the Email Reminders tab.
If you want to stop an Email Reminder from running, click Cancel Email. If the Email Reminder had been set up as a draft, this link would say Delete Email instead.
To edit the Email Reminder, click on its subject line under the Notification column.
You will be taken into the 3-step wizard where you can make the necessary amendments to the Email Reminder.