How to delet photos?
Like Carl P said, tap and hold an album, and then you can see "Select all" on the bottom, tap it and press "Delete" to remove all the files.
Also, you can try another free app - Apowersoft Phone Manager. This app also has the function to delete files. Open this app on your phone and go to "Photos", hit "Select" > "All" and then tap the delete button on the bottom left to remove all.