After more than 15 years of successful data taking, the Pierre Auger Observatory started a major upgrade, called AugerPrime, whose main aim is the collection of new information about the primary mass of ultrahigh-energy cosmic rays, besides adding new indications on hadronic interactions at energies much larger than those reached in human-made accelerators. The upgrade program includes: the installation of a plastic scintillator detector (SSD) and of a radio antenna on top of each water-Cherenkov detector (WCD) of the surface array, an extension of the dynamic range of measurement through an additional small photomultiplier tube inside the WCD, new electronics to process signals from the WCD and the SSD with higher sampling frequency and enhanced resolution in amplitude. An array of underground scintillator detectors will measure the muonic component of lower energy extensive air showers. After presenting the motivations for upgrading the Observatory, an overview of the detectors is provided, together with the deployment and commissioning status.