[Rwp] How does eq works - cutting frequencies off guitar amp tracks.

[Hadi]

Hi guys
I want to learn to work with eq, and try and cut off  extra frequencies 
that my guitar amp output has. but I don't know how it works, I actually 
don't know even the basics.
For example, my friend says that My guitar amp tracks have extra highs, 
and I have to use a low pass filter cutting 5 to 7 KHZ. How may i 
achieve this?
Is it accessible to work with EQ even?
Thanks for any input
Cheers
Hadi