Your clock has a floating balance movement. The adjustment for the speed is on top of the little wheel that rotates back and forth. The adjustment is a little 3 finger lever on top of the wheel. You will see stamped on the brass plates which way to turn it. + increase speed and - for decreasing speed. Do not try to adjust it to much. The maximum adjustment will be about one quarter of the wheel diameter. You only need to move it about 1/32 of an inch to begin to make a difference.
Stevens Clocks
June 2010