Bicycle Road Tyres
Mountain bike and road-bike rims vary diameters and use tires which can be different diameters. Specifically, mountain bicycles utilize 26" tires and road tires make use of the ridiculously meaningless 700c size. I will not enter into exactly what these sizes mean here, but you can find more info on this web site or, in the event that you really want to dork completely for slightly, read Sheldon Brown's page on tire sizing.
As Batman pointed out, you can buy slicks and semi-slicks for 26" rims. They truly are not officially "road" tires - they're a little larger and run lower pressures - nevertheless they however reduce moving weight. There are several options. Only shop around
All of that stated, i am unsure everything find uncomfortable regarding your hill bicycle tires. Mountain cycle tires are typically much more comfortable than road bike tires. A very important factor you may start thinking about is probably decreasing the pressure inside tires. The maximum force noted on the side is extremely frequently greater than you desire or need. You can read more about finding the correct pressure here.