There is currently no way to delete groups of shows. But this is one of the most requested features,so I would think it would be developed fairly soon.
To delete a timer in the web browser, go to Scheduled, and then bring up the show. You will have either REC ALL or REC NEW highlighted. Just click on the highlighted one to set it to not record anymore. Once you click on the X in the top right corner of the show, it will disappear from the Scheduled page.