The present paper presents a theoretical study of the advanced assessment implementation methodology through the application of a Structural Health Monitoring system (SHM) to update the level of seismic risk of existing bridges. Since seismic risk is defined as the economic impact of an earthquake’s damage, both mitigation and constructive measures should be implemented in order to reduce the damage when such extreme event occurs. To this end, in existing bridges placed in areas with a high seismic activity, an advanced assessment should be carried out. The evaluation must be done not only in those which are considered of major importance in an emergency case but also all those that may be susceptible to be indispensable when the main ones might suffer severe damages that may render them unserviceable. Therefore, it is about to assess the importance and feasibility of implementing a SHM system such that the status and real behavior of the bridge in front of extreme events (earthquakes) can be known. With the results obtained through the SHM system, different parameters that can define the level of seismic risk of the structure can be updated. This evaluation would allow to compare and propose different options of repair and / or maintenance in order to increase the capacity of the bridge and thus to reduce the seismic risk of the structure. Then, an optimization of the resulting costs would be possible.