If this is a RA90, the unit number is via the front panel of the RA90.
In the upper left of the panel, there should be a small hole in which
you can stick something like a toothpick or paper clip.  Insert such
a thing in there and press.  The front button will now allow to modify
the unit number.  I can't remember which do what but experimentation
should reveal want to easily enough.

Matt Thomas               Internet:   matt@3am-software.com
3am Software Foundry      WWW URL:    http://www.3am-software.com/bio/matt.html
Westford, MA              Disclaimer: I disavow all knowledge of this message