How to delete 400000 plus screenshots from an iphone.... phone keeps freezing!

If she's using iCloud photo library, log into her iCloud account in a browser on your computer and delete them from there (you'll need to do it in chunks to make it manageable). Empty the recently deleted folder as well.

The deletions will sync to her phone.

"How to delete 400000 plus screenshots from an iphone.... phone keeps freezing!"

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Deleting Screenshots form iPhone:

A1."My daughter has somehow accumulated 440000 screenshots over the years on an iphone. Her prevous phone was traded in and she upgraded to a new iphone without as much storage as we were assured that it would not be an issue to delete the data and set up the new phone..... that isn't the case."

B1. These are showing up as taking up space in iPhone Storage because they are locally-stored. Does she no longer need those screenshots? IF so, transfer them to a computer, and then drag them to the Trash, finally emptying the Trash. Note that it might take a few for the deletion of 400,000 screenshots. If you disconnect the phone from the computer while in the process of moving them, then it would stay queues in the deletion, and you'd have to reconnect it. So, keep both the iPhone and the PC powered on, while performing this.

1. Go Here: Transfer Photos and Videos from your iPhone or iPad to your Mac or PC - Apple Support
2. Scroll to: Import to your Windows PC

Q2. "We only have access to windows laptops to help with the process. Is the only option we have setting up a new apple ID? we can't delete from the phone as files keep reappearing. We did manage to delete 40000 initially. between us we have 2TB of icloud data most of which is used for storage of her photos!"

A2. A photo can be up to 4MB in size. One thousand of those would be 4GB. Multiply that by 400 and you'd getting a presumptuous 1.6TB of space taken up. So, trash these, if no longer needed. Elsewise, it's a matter of sorting through them.