If you need to delete a subscription trip for any reason, just follow these steps.

Find a trip that you want to delete the subscription and select "View details".

If it is a subscription trip, click on "View Parent Trip".  This will take you to the original trip that the subscription was created from.

Scroll down to Subscriptions to find the different occurrences of that subscription.  Click on the "minus sign" under the "Actions" column.  

On the Delete Subscriptions page, you can view all of the currently generated subscription trips for the future days.  Select all of the trips you want to delete.  You can also choose to delete only specific trips if you know a subscription is going to end by a certain date.  If there are any other related subscription trips that you want to delete, click on "Delete Related Trips Subscription".

A new section will expand with all of the related subscription trips.  Select the subscriptions and then select the trips you want deleted.

Once all of the subscriptions and individual trips have been selected click on "Delete Subscription and all selected trips".