Make sure to first have SuperBLT installed. Click the link in the dependency list.
Optional video tutorial for installing SuperBLT, BeardLib, and mod_overrides mods: https://youtu.be/rin_sjSJIkg
After downloading the mod, use a program such as 7zip or WinRAR to extract the main folder of the mod.
Drop that folder into the mods folder which is supposed to be in the game's installation folder (don't know where that is? click here)
mods
after downloading unzip file with 7zip or WinRar
move skill tree background restoration folder to mods
move Nikki Ann-Marie Skill Tree folder to mod_overrides