To install:
- Drag and drop the update folder from the archive into your GTAIV.exe root folder

If you are using Shvab's LibertyCityPlates mod, follow these instructions instead:
- Drag and drop the update folder from the archive into your GTAIV.exe root folder
- Go inside the update/DLC folder and delete DLC.img
- Go to the Dynamic License Plates (optional) folder in the archive
- Drag and drop the DLC_LibertyCityPlates.img from the archive into the update/DLC folder

Link for the Dynamic License Plates mod:
https://gtaforums.com/topic/998667-libertycityplates-license-plates-for-iv-and-other-things/