It's not stock. You replace the 52t upper with a 54t upper. For 9 speed systems, salsa makes a chainring. See sheldonbrown or nashbar. You also replace the low end. Last time I replaced a 30t with 28t, but now need to go lower. I wan thinking of a new drive train of 24-39-54 x 11..28. However, in reviewing the gearing, nothing is gained by the 39t middle, and if can get 24-54 x 11..28 to work, I can change from a triple to a double.

A 110mm is only available with 33t, but a 74mm will go down to 24t. Don't know if there is a 110mm to 74mm adaptor. I seem to recall someone mentioning this was available, but I have lost the reference.