What is the ruling on a witness increasing the deceased's salary in order for his family to receive greater insurance?

Your testimony that the deceased's salary was 1300 pounds, when it was only 300 pounds, is a false testimony and one of the gravest major sins, for the Prophet, peace and blessings be upon him, said: "Shall I not inform you of the greatest of the major sins? Associating partners with Allah, disobedience to parents, and indeed, false speech and false testimony." This testimony is not permissible on account of the man's sisters being minors or the family's need for money. The sin is even greater if you swore an oath upon it, making it a perjured oath (yamin ghamoos). You must repent immediately, and a complete repentance includes compensating the insurance company for what the family took unjustly, unless the company forgives you.