Before install please make sure you have Beardlib, SuperBLT, and Custom OST installed.
Beardlib and SuperBLT Tutorial by b33croft: https://youtu.be/O_pGk5UGrCo
Custom OST Tutorial by Hugo Guerrier: https://www.youtube.com/watch?v=VrL_LDNTMPI&t=335s

Once you've completed the setup for these mods use an archive application such as Winrar or 7zip to extract the mod folder from the zip file. Find the CustomOSTTracks folder and place the 115 Mod folder into it.