You can delete any alert you created. To delete an alert that another user created you must have the Edit Alerts permission set to Create and Edit All.
Once an alert has been deleted, it can't be restored. Proceed with care.
Select Customer Setup > Alert Control.
Enter your search criteria:
Choose the Alert Type from the drop-down menu.
Use the Message Contains field to narrow down your search based on the alert message.
Add the Display Options by selecting the corresponding boxes the alert appears.
Select the Alert Date Range:
Create Date: The date the alert was created.
Effective Start Date: Corresponds to the Effective Start Date on the alert.
Effective End Date: Corresponds to the Effective End Date on the alert.
Click the Search button.
Select the alert.
Click the Delete button.
To confirm, click Delete again.