You can have as many as you'd like, but to see all that you're subscribed to and edit/delete some, click on "settings", then look for "bookmarks" on the left of that next page. There is a check box to the right of each one that you're subscribed to. Put a check mark in each one that you'd like to delete, then scroll down to the blue button "selected threads". In the new box that pops up, put a dot in "delete subscription", and click "Go".