Learning to safely climb the stairs in your home is a great accomplishment for your Bulldog puppy. You can start working on the stairs from a very early age (as long as your Bullie is tall enough to reach).
Using training treats is of course very effective. Place a treat on the edge of a stair just in front of your puppy. If he doesn't see it or is not interested, lift his front paws up onto the stairs so that he can reach the treat. He will happily oblige you by eating the treat. Work on this until your puppy knows there will be a treat on the stair. Soon he will be rising up to put his front paws on the stair on his own to get the treat.
Once he has this down, move the treat back a bit further on the stair so that he has to stretch further to reach his treat. At this point start with your puppy to one side of the step and the treat about one foot to the other direction on the step above. Continue this process until the treats are far enough back that he has to climb or jump up on the stair to get it. If he can't or is unwilling to give him a helping hand until he gets the idea on is own.
Your puppy should be going from step to step at an angle (this makes climbing easier and decreases the likelihood that your puppy will stumble head-over-heels when you teach him to walk down the stairs).
Next, create a trail of treats up the stairs at an angle. Your puppy will then learn to take several steps to get his treats. Over the course of training, gradually decrease the number of treats on the stairs so that he has to climb 2 or 3 before he gets rewarded.
Teaching your puppy to climb down the stairs simply requires starting at the top and placing treats every few stairs (at angle). It is strongly recommended that you position yourself on the stairs just below your puppy. In the event of a stumble, you'll be there to prevent injuries until he is more proficient. Going down seems to be more difficult with little puppy legs than going up, so give it time.
Eventually the ability to follow you up and down the stairs will become reward enough for your loving friend and you'll no longer need to use treats. Keep in mind that this process may take several days. Keep the training sessions short. It is not necessary to rush your puppy.