This is a relatively common question, often spurred by the desire to replicate the taste of commercially available "lite" beers.
However, these beers differ notably from craft beers and homebrew in that they rely heavily on rice instead of barley to produce fermentable sugars. By using rice, these beers are light on calories, but also lack the character and flavor of a good craft beer. Therefore, there's not a great way to make a "lite" beer while maintaining all of the many desirable attributes of craft beer.
A good compromise is generally to use rice syrup solids as a substitute for a portion of your malt extract. The more rice syrup solids you use, the fewer calories your beer will have, but it will also have less flavor. Generally, we recommend keeping rice syrup solids below 15% of an intact craft beer recipe, but a greater proportion can be used if desired.