You said you had a flat. Did you let all the air out of the tire? I have Kenda 26x4s and they are so big an soft they are just about the easiest tires to get on and off the rims. You barely need tire levers. (Find out what tire levers are. Google is your friend. Don't use a screwdriver! And seriously, search you-tube for a couple of videos on changing a bike tire. There are probably about 3000 of them, and they all explain it better visually than just about anyone can do here in words. I like Park Tool videos.
Park Tools How to Change a Bike Tire
TT