Step one: For the start, it's nice to change the color of your bike. Take it to the shop, or do it yourself if you want to save some money.
Step two: Get measured by an expert. After that, you can have your pedals, seat, and handlebars adjusted for a more convenient ride.
Step three: Buy a brand new seat that is wider, narrower, or has built in gel padding for extra comfort.
Step four: Add some storage space with a saddle, backpack, basket or small cart. Check for something that is waterproof, and that can be locked up same as the rest of your bike.
Step five: Change the old tires. Add fenders to protect against rain water and flying mud.
Step six: Add some accessories and attachments, something like LED lights, a bell, a mirror, or a compass.
Step seven: Upgrade your style to harmonize your new bike with a new helmet or matching gloves before going on the road.