I presume you meant to say V27 and not V17. I also presume you have a MkIV unit to accept the V27 software.

Here are the instructions:
1. Turn the ignition switch to the first position. Let the navigation system boot up and get into normal operating mode.
2. Leave the system on (never turn the power off during these steps!!)
3. Go back and eject the map CD from your drive unit.
4. Put the V27 disk into your drive unit.
5. Watch your screen and be patient. It says it will take about 6 minutes to do the upgrade, but it doesn't take that long. The following will appear on the screen..

screen 1: CD-ROM in navigation computer. Loading software.
screen 2: Software Update
The installation program will update your navigation system!
screen 3: Software Updated
Update is complete! At this time press the right knob to continue on this screen.
screen 4: Software update
The system will reboot now! In a few seconds, it will start up with your new configuration!

6. When it's done it will eject the CD automatically.
7. Put your map CD back in the drive and make sure everything is working properly.

Enjoy the new software. If everything appears to work well.. which it should then you will be able to activate the Perspective view which involves another set of instructions.

Let me know how you made out and I'll provide the next step.