What do I need to do to uninstall / re-install EasyRoutes?

All you have to do is uninstall EasyRoutes like any other Shopify app (here's a link to Shopify Help Center). Note: Uninstallation also will automatically cancel any active subscription plans you have with EasyRoutes. 

Is there any code to uninstall?

EasyRoutes does not inject code into your theme or into your liquid files, and we don’t interface with your theme, just your orders.

The exception could be that if you have edited your email notification template to include Photo Proof of Delivery photos.