drop the rockford_plaza_retextured folder to 

Grand Theft Auto V\mods\update\x64\dlcpacks

then edit dlclist.xml found here Grand Theft Auto V\mods\update\update.rpf\common\data

add this line to the bottom of your packs in dlclist.xml        <Item>dlcpacks:\rockford_plaza_retextured\</Item>

