Unzip "units_sharpened.zip" into the "Original" folder, rename the "units.bmp" file to something else (e.g., "units_old.bmp") and rename the "units_sharpened.bmp" to "units.bmp".
Back up all the .spr files then delete them from the directory. Then the new unit graphics will work.

One thing I've noticed: the unit sprites as shipped have a nice feature of some areas bearing the nation's color (sails on triremes, for example). Once you remove the .spr files and use the .bmp file instead, you lose that feature.

This file may be freely distributed; I assume no responsibility for anything, etc., etc.