I switch my American Bulldog pups to adult food between 4-6 months of age. My Olde English Bulldogges are switched at 6 months of age. Large breed dogs can grow too fast on puppy formulas and it's best if they be taken off of a puppy formula by 6 months or so. Failing to do so can lead to bone and joint disorders such as dysplasia, etc. or arthritis later in life. Your pup is 8 months and it would be perfectly fine to switch over to an adult formula now.
I was told to get both of mine off puppy food at 8 months. My girl was getting a little too pudgy for my vets taste and he actually told me to start feeding adult light. Obviously as a bulldog owner, you know how important it is to keep their weight down. Lots of people really want the "fat" look. I'd rather have healthy dogs.