Out comes the 5400 RPM, 500 GB, SATA II mechanical hard drive, provided by HGST (a Western Digital subsidiary).
With just a single screw securing the caddy, replacing this drive is easy-peasy.
Not only is this hard drive user-replaceable, but it's a standard 2.5" (a.k.a. laptop-sized) SATA drive, meaning you can replace or upgrade your storage with any off-the-shelf drive you like, so long as it meets these standards: no thicker than 9.5 mm, and no smaller than 160 GB. Users rejoice!