How to install AR 15 lower parts kit?

It depends on the lower parts kit. Some kits come with a bolt carrier group and charging handle, while others don’t.

First, you need to remove the pistol grip and selector switch from the old lower receiver. Once those are removed, install them on the new lower parts kit. Next, install the takedown pins, buffer tube, and stock. Finally, install the bolt carrier group and charging handle. See your specific kit’s instructions for more detailed instructions.