How to change a bike tire.
1. Open rear pannier. Take out bike jack.
2. Jack up bike after making sure the emergency brake is set, unless it's a fixie. To be safe, put a rock under the wheel not being repaired. Also helps to have a good kickstand.
3. Take out spare wheel from rear pannier. Undo quick release skewer on affected wheel. Rear wheels are trickier because of the bike chain. Make sure you have both a front and rear spare wheel in case either gets flatted.
4. Take off flatted wheel, exchange it with proper spare, tighten skewer, lower bike jack, toss away the rock, and put everything back in the rear pannier.
5. Take flat to bike shop so they can change out the tube and/or tire.

No so difficult, really.