My iphone 4s is broken and i want to delete personal files in it?

How do i do that? Its an iphone 4s, my mum's gonna fix it somewhere and will use it on her personal use at a diff country and i don't want her to see my.stuff

Well, if its not working, you can't

even if that phone is connected to iCloud there's no guarantee you can remotely delete what's there even after its repaired

anyway

who the hell would bother spending money on getting a 4s repaired

sure, if the screen was cracked or something but if its not turning on. Meh. Forget it, move on unless its an issue you can deal with yourself

Go to your iCloud account via any browser and use Find My iPhone to wipe your phone

If or when your old phone gets repaired and connects to a data service it will immediately wipe itself back to factory specs. In reality all your data will remain but the memory locations will be flagged as available for reuse and the remaining data will be securely encrypted and unrecoverable in any meaningful form.

Probably not worth the cost to get it repaired
and hwne it is repaired, then is the time to go in and reset the phone.

You also need to remove 'your' appleID
and the new owner put their 'new' appleID on it
Otherwise, it remains locked to your AppleID (and password) on iTunes etc
(it is a security feature but will catch people out selling / transferring phones)

Better to spend the money on getting a refurbished iPhone 5c etc
(more powerful, and still supported by apple - just)

You also need to check that the iPhone is unlocked for any network
(almost) All iPhones are locked to the 1st network they are used on.
and you have to ask for them to be unlocked (at a cost)

Yes, a little shop on the corner can 'hack' an unlock, but unless it is officially unlocked from Apple, it can lose that when it is reset or reloaded with an update.