To clean your Napa shoes you can easily wipe the stained area with a damp cloth and they will be as good as new.
Remember to remove the laces and let shoes dry naturally without exposing them to the sun or radiators. Extreme heat to dry them is not good for them.
Occasionally you can use colourless waxes (even the one you use for your hands if it doesn't have dyes in it!) to keep the skin moisturised and increase its durability.
NEVER put shoes in the washing machine.