Reactive synthesis is an automated procedure to obtain a correct-by-construction reactive system from its temporal logic specification. GR(1) is an expressive fragment of LTL that enables efficient synthesis and has been recently used in different contexts and application domains. In this paper we investigate the dynamic-update problem for GR(1): updating the behavior of an already running synthesized controller such that it would safely and dynamically, without stopping, start conforming to a modified, up-to-date specification. We formally define the dynamic-update problem and present a sound and complete solution that is based on the computation of a bridge-controller. We implemented the work in the Spectra synthesis and execution environment and evaluated it over benchmark specifications. The evaluation shows the efficiency and effectiveness of using dynamic updates. The work advances the state-of-the-art in reactive synthesis and opens the way to its use in application domains where dynamic updates are a necessary requirement.