Assuming the derailleur hanger is straight and the rear derailleur is set up according to the manual, the barrel adjusters may be used to improve shift performance.
If you are experiencing slow shifting from a larger cog to a smaller cog (outboard shifting), turn the shifter's barrel adjuster clockwise in 1-click increments until shifting is correct.
If you are experiencing slow shifting from a smaller cog to a larger cog (inboard shifting), turn the shifter's barrel adjuster counter-clockwise in 1-click increments until shifting is correct.