Yes!! CTRL+F1 did the trick!
I now have access to the timing values and was able to set them to 4-4-4-12. I also see another group of values - "Advance Timing Control" - containing 7 items, like "ACT to ACT delay" (value=3), or "Rank Write" (value=3).
Is it enough to change the CAS, RAS and tRAS values (4-4-4-12) or these other 7 items can changed too?
thanks a lot for your answers so far!