Which step involves removing a port's existing mapping in the DMR?

In the context of managing port mappings in a Data Management Report (DMR), removing a port's existing mapping is specifically accomplished by deleting the existing mapping. This step is essential because it clears any previously established associations that could conflict with new configurations or changes being made to the system. By deleting the mapping, the system is then free to create a new mapping without any residual conflicts from the earlier configuration.

For effective port management, you often need to ensure that the port’s past settings do not interfere with the setup of different functionalities or different ports altogether. This step is vital especially in environments where port configurations can change frequently due to updates in technology or operational requirements.

The other options, while they may relate to port management, do not directly address the requirement of removing a mapping. Re-mapping to a different port suggests making a new connection without clearing the old one, navigating to the Limitation window pertains to system constraints or capabilities rather than directly modifying the mapping, and updating the firmware typically deals with software enhancements rather than specific port configurations.