  The GREGOR telescope was inaugurated in 2012. In 2018, we started a complete
upgrade, involving optics, alignment, instrumentation, mechanical upgrades for
vibration reduction, updated control systems, and building enhancements and, in
addition, adapted management and policies. This paper describes all major
updates performed during this time. Since 2012, all powered mirrors except for
M1 were exchanged. Starting from 2020, GREGOR observes with diffraction-limited
performance and a new optics and instrument layout.
