1.First make sure you have OpenIV
2. Navigate In OpenIV to (Steam\SteamApps\common\Grand Theft Auto V\x64e.rpf\levels\gta5\vehicles.rpf\)
3. Click FILE and enable EDIT mode
4. Drag and drop the interior ytd file from whatever color scheme folder you choose.
5. Also Drag the vehicles_cav_interior.ytd file over into OpenIV
6. Open GTA 5 and Enjoy