I'm assuming that the number indicates that there's a notification for the relevant app. Pull down from the top of the screen to see all notifications. if you want to respond to a notification, tap on it. Otherwise swipe it sideways to get rid of (and, at the same time, the number on its icon).
With regard to removing downloads from the BBC Sounds app, have you tapped 'Delete' after swiping left?
https://www.bbc.co.uk/sounds/help/questions/downloading/delete-download