In reply to Lorraine McCall:
They will fit on the metal wheel rims (perhaps some effort required if known for being a tight fit) but you need to see how much room there is on your frame and fork to take a larger tire. What bike do you have?
Look at the gaps between your frame at the back and the rear tire. Is there room for another 3mm of tire? Same at the top of the fork at the front?
A larger tire should give you more comfort as you can inflate to a lower pressure. You won't notice the minor decrease in speed I'm sure. I run 32c tires on my bike and it zips along nicely.