In Gmedia Library select images you want to delete, then click Action button and choose Delete selected items.
If you want just delete images from Album (which are in Gallery), but leave them in Library – > select images in Library -> click Action button choose Move to Album -> assign different Album or choose No Album for selected images.
To sort images in Album go to “Album, Tags..” page -> click Album title to edit it -> set Order option to User Defined -> Save -> sort images with order field or choose “Drag’n’Drop sort in Action menu -> Save Album.