The 'take-make-dispose' consumption model that remains shackled to the global economy, is also affecting production assets. Industry is promoting the transition to a circular economy (CE). Deployment of the evolving digital technologies and realisation of Industry 4.0 (I4.0) enhance machines automation, connectivity and provide large amounts of data that can be interpreted in a way that were not possible before. It offers to companies the opportunity to retrofit their legacy equipment that cannot meet the constantly increasing market demands. This helps to extend the useful lifetime of this equipment and accelerate the transition to a CE. However, Industry is still lacking an efficient systemic multi-level approach that enables a cost-effective, holistic, and integrated application of CE principles to the digital uplifting of factory 4.0 capital investments. Companies and particularly SMEs face diverse challenges for implementing I4.0 systems in their businesses due to lack of knowledge, expertise and investment. The translation of CE strategies into concrete actions will help professionals to consider circularity measures in a broad sense. This paper introduces the 10 Circularity Protocols for extending the useful life of large industrial equipment, addressing issues at product, machine, and process level. With guidance on the application of I4.0 technologies, the Protocols help to digitally reengineer outdated machines to be more productive and energyefficient, to decrease maintenance downtime, spare-parts storage and off-spec pieces. The Protocols also support on the End-of-Life (EoL) management of the different machine components that are not technically, economically and environmentally feasible to be reused or repaired. As a final step, the future research line and methodology focusing on the digital implementation of the Circularity Protocols guidelines for their deployment and validation in real industrial cases is introduced.