If you would like to avoid the xposed framework like I do then download advanced apk tool, decompile framework-res.apk and after you decompile it then go to /res/values/dimens.xml and modify navbar height dpi there. After you're done doing this then recompile, sign and zipalign and push into the device. Superuser mod is a must before doing it.
My work on xda and things I'm proud of:
Single link for that as the sig got too big ^^
If you want me to reply then please quote my post or mention me by writing @olokos. This way you can be sure I'll reply.
sooner or later :P