According to Intel's website, the i5-6400T is supposed to run at 2.2GHz with a max speed of up to 2.8GHz if the CPU is being stressed. There is no way to improve clockspeed beyond that.
If you are actually referring to responsiveness, then I am guessing you are noticing the difference between a PC with a standard hard drive and SSD (solid state drive). SSDs have much faster read / write speed than a hard drive so things like boot up the PC or starting up a program will be done faster on a PC with a SSD because of the much higher read speed.