int setPinValue;
int parameter;
if((setPinValue>=240)&&(setPinValue<420)) //"Down" button pressed
{lcd.clear(); parameter--;}
Where does setPinValue get valued? Where does parameter get valued? This code snippet does not provide enough information.
Your topic says "lcd.clear() doesn't work", but it looks more like it ought to say "lcd.clear() doesn't work because I don't call it".