[Style] Flexfile Dark Is Outdated, How Can I Update It On My Own Hand?

Hey guys! I'm currently trying to get a good looking style on my website but almost every style that I like is outdated and i'm trying to update the Flexile style on my own hand but I'm not sure how.
The Flexile is outdated and i'm using Xenforo 1.2 and therefore the website looks like this:

Can someone explain how I can fix this/update a theme on my own hand?
Thank you.