The screenshots is stored on SD card,If you need to delete the screenshots to free up some space, Follow the below step by step guides:
1)You can use the “My File” apps to access your SD card, Launch ‘My File” Apps from the “Apps drawer”
Now, You can find all the screen copy pictures.
Tap and Hold one picture you want to delete, It will popup a window, Tap Delete and then Tap Ok to confirm the delete.
If you want to delete all the screenshots stored on SD card, From Screenshots folder screen, Tap Setting,> Tap Delete,> Tap Select all, > Tap ‘Delete” > Tap Ok to confim the delete!
Now, You have delete all the screenshots stored on SD card, But some of the screenshot still stored on “clipboard”.
This is the guide to Delete screenshot stored on clipboard