Issues updating from 3.1.3 to current 4.3.1

I offered to help a friend update his website. Little did I know that his WordPress was ancient.

I’ve had a multitude of issues, but the one I’m stuck on right now is the actual update. I loaded everything through Filezilla. There were about 50 failed transfers, and it didn’t update the WordPress at all.

Any help? The tech support through the host is a joke, so I’m hoping someone here could lend a hand.

Thank you!