How do I recover what's left of a file that has been deleted but not completely over written? Let's say the deleted file is 10mb 5 of those have been overwritten I want to restore the remaining 5. Thanks!

How do I recover what's left of a file that has been deleted but not completely over written? Let's say the deleted file is 10mb 5 of those have been overwritten I want to restore the remaining 5. Please help? Thank you!