If you go to "media", then "your media" or "your content" and you can delete them from there.
Hovering over them should let you select them on a pc/laptop - tick the boxes of the one you want to delete, then you should be able to delete the "Selected" ones. (Selected button at top right)
From a mobile/tablet, the checkbox should be visible straight away.
Be aware that the space won't be freed up immediately - this is usually done when the photos are physically deleted from the server overnight.
It is also possible to upgrade your account for £5/year (or included as a contributor) to allow 150MB of photos instead of the default 10MB. This contributes towards the extra storage and backup space costs that I have to pay.
If you become a contributor you get a nice flashy badge next to your username. Would look great next to yours. Also you can feel all smug and superior over the rest of the users, more than worth the money I say