To remove particular media items from a Media Gallery album:
Open the album and make sure you are in Grid view.
Hover over the media item to be deleted and click on the Trash icon that appears to the top-right. The media thumbnail should turn semi-transparent as a result (clicking on the red minus icon de-selects the item).
Repeat this process for any other media files contained in the album that you wish to delete.
When you have completed your selection, proceed to the bottom-right corner of the album window where you will see a summary count of the items selected, and an "Undo" and "Delete" button:
- Click "Undo" to clear your selection of all files flagged to be deleted.
- Click "Delete" to proceed and delete all the flagged files.