In Page view, display the thumbnail page of the gallery you want to remove.
Select the photo gallery object and delete it.
Go to Site view.
Delete the photo page associated with the gallery.
When you add a new photo gallery, the name of the gallery you just removed still appears in the Insert an existing Photo Gallery list in the Add Photo Gallery dialog.
To delete a photo gallery completely from your site:
Go to Assets view.
Select the Data Objects tab.
Select the photo gallery you want to delete.
Press Delete.
You can delete a photo gallery only if you have first removed it from your site as described above.