Yeah, you can use a range of tires with one rim size. The current tire size doesn't help you though, you need to know the inside diameter of the rim.


Here's a useful article when you find your rim size. The chart in the article is in millimeters.
http://www.sheldonbrown.com/tire-sizing.html

Here's another article which has a (rather small) chart with sizing in mm and decimal.
http://www.biketiresdirect.com/tire-width-article