Old Kitchen Exhaust Fans - Advice Please?

[Todd Kalsey]

Hi Everyone!  I'm currently updating a unit in a duplex and was wondering what to do with the old kitchen exhaust fans.  The one pictured below is okay at first glance, however the interior is nasty with probably 40-50 years worth of cooking grease/exhaust built up.  The fan in the other unit is 50x worse and is a total eye sore.  Anyone have any experience and/or suggestions?   We're trying to update everything and give the units a new/clean look, but attempting to avoid serious gutting on issues.  Thanks in advance!