Hi,

This is what worked on mine (I'm using Firefox, not sure if the different browsers impact the process)

When you go into the album you should be able to see the thumbnails of the pictures included in the album

Click the picture you want to remove

That should bring up a larger copy of your picture along with options including
Edit picture
Add to group
Report picture

Choose edit picture

That should bring up another page with a text box, thumbnail of the picture and the options to mark the picture for deletion or to add it as the album cover

If you check the delete this picture option and press save changes it should remove the pic for you