There isn't any rear speaker wiring in the Uno Mk1 as standard. I seem to recall you have a Mk1 (most Unos in NZ are). I don't think there's any rear speaker wiring in the Mk2 either...
I'm not sure if you meant "anyway, I might re-wire it" or "any way I might re-wire it?" Classic case of why punctuation is needed!
The first one is a good idea.
If you were asking the question - just get new speaker wire from Jaycar, Dick Smith, etc. Six metres should do it. Either attach crimp terminals for the speakers, or get some wires that come with speakers and extend them (solder the connections and insulate, or use terminal blocks).
To install the wires, fold the rear seat. Remove the rear shelf supports. Thread the wire behind the plastic or carpet trims on the rear wheelarches, then under the boot floor beneath the rear seat. Remove the door sill carpet holders front and (for a 5-dr) rear, and run the wire under the edge of the carpet, then tie up under the corners of the dashboard and thread across to the centre (stereo) console.
Most Japanese stereos use green/green-black for the left rear speaker, and purple/purple-black for the right rear speaker.
Cheers,
-Alex