you get your PLL model selected, click on "Read Clocks", then open the
"PLL Control" window. Notice that the number of sliders depends on the
PLL model features. Some models also only support a predefined set of
frequencies, and therefore may show a "step-by-step" slider.
Once your new clocks are choosen, clock on "Apply Selection" to
make them effective. If you want to come back to current values, click
on "Reset Selection".
The "Clocks" window shows the current clocks in real time. It is
independant from the selection window, so it will tell you if the new
clocks were really applied.
Notice that the CPU clock may vary if the CPU uses a clock
modulation mechanism, like C1E or Speedstep. Load your system if you
want the CPU to run at full speed.