Basically, you just need to replace the map data : see tutorial here :

http://forum.xda-developers.com/showthread.php?t=1007132

TIPS from selphy :
Ok, for those of you who have trouble installing the Google Maps (for Navigation), i had issues too, but managed to do it through the following:

1. First, make sure your phone is rooted, then download the Google Maps-ownhere.apk (NOT the re-sign one), and transfer to your external SD card.
2. Using Titanium backup on your phone, wipe data and then uninstall both Google Maps and Street View.
3. Then using root explorer on your phone (i used Super Manager, which also has root functions), transfer the Google Maps-ownhere.apk file to your phone's system/app folder (make sure its set to R/W).
4. Then just reset the phone, and voila! Navigation is available!

There is probably an easier/shorter way, but this works for me. Hope it helps


ALTERNATIVE tips from user Alamaklor :

[GUIDE] How to get Google Map 5.7 (nav) to work

If you are getting "Application not installed" when installing Google map 5.7, here's what you need to do:

1. In Titanium Backup, select Maps and make a backup.
2. Select Maps and wipe data, then uninstall.
3. Select Street View and wipe data, then uninstall
4. Download map5.7ownhere-signed.apk from here: http://www.filesonic.com/file/1389928264/m...wnhere-sign.apk
5. Copy the file to /system/app using root explorer (or any "root" explorer)
6. Mount system as R/W
7. Install Google Maps 5.x ownhere-signed.apk
5. If you wish to reinstall streetview, download it from here: http://www.freewarelovers.com/android/app/street-view (doesn't work in Msia, as you should know)

One "bug" I noticed google nav has is that it automatically sets the system volume to MAX, but it wouldn't turn it back down to default volume when it quits