To disassociate Google Photos from an email address and delete all photos, follow the steps below:
Delete the Google Photos app, the camera roll photos will not be affected.
Go to Recently added where photos are sorted by upload date.
On a mobile browser, long press the first photo and keeping the screen pressed stroke down to select a batch then move to trash. Medium size batches are best rather than trying to select all at once.
On a computer, point at the item(s) you want to delete. At the top left, click Select .
Alternatively point at the Added date(s) and click Select .
Page down 10 or so times
press and hold down the Shift key on the keyboard.
keeping the shift key held down, move the mouse and the photos will turn a blue shade.