Background: The Kilometer-square Array (KM2A) is one of main detector arrays in the Large High Altitude Air Shower Observatory (LHAASO). Thousands of detectors and front-end readout electronics spread over one square kilometers. In such a large-scale

dispersed high energy physics experiment

a flexible

efficient and reliable system for remote update of FPGAs (Field Programmable Gate Array) becomes significant. Purpose: This study aims to introduce a scheme to update FPGAs of the front-end readout electronics and reload firmware online without extra circuits while ensuring its reliability. Methods: The remote update based on MultiBoot and reload logic based on Internet Content Adaptation Protocol (ICAP) make it possible to update the firmware of all the FPGAs simultaneously. Results: The scheme proposed in this paper has successfully applied to the detector arrays in Yangbajing

Tibet. Its flexibility

convenience and reliability has been proved by the stable operation since October 2014. Conclusion: Remote update scheme based on MultiBoot makes it possible to update FPGAs without any extra circuits

thus literally reduces the cost of electronic systems while guaranteeing the reliability. Abstract