cursor moving while typing

I use a hp probook 4520s at my school where I teach. I love all about it EXCEPT that I'll be typing along and it will jump back up in the text to another place. Usually it's where I will be typing and stop to think for a minute and it jumps back up in the text to a place where the same letter as the last letter I typed and then without realizing I go on typing and half my word is up in a wrong place. Very frustrating. Where is a setting to stop the computer from thinking it knows more than I do about where I am typing at? Or a way for it to not be so sensitive on the touch pad? Sometimes I think maybe it's picking up and dragging cursor from my hand just moving above it.