In TFS you can use Project Alerts or Alerts Explorer to edit your subscriptions. You will not see subscriptions created by others.
To see all subscriptions you could have a look at the tbl_EventSubscription table in the collection database (Caution: Do not make any changes to the TFS DBs!).
To find out which user identity is hidden behind the GUID in the "SubscriberId" column, you can use the following SQL statement
FROM tbl_EventSubscription es
JOIN [Tfs_Configuration].[dbo].tbl_security_identity_cache sic
ON sic.tf_id = es.SubscriberId
WHERE es.Id = 123
where 123 is the Subscription ID (see "Id" column in the screenshot above).
(Thanks to Patrick Carnahan from Microsoft for helping me out with this and providing the SQL statement above)