I have always heard and now teach, move the rear site, in the direction that the impact needs to move. Shooting low, the impact needs to be up, so move the rear site up.
I would caution a new shooter that adjusting the sites needs to be the last thing they try. New shooters seem to want to jump to the reason they are not hitting the target in the desired place is because the stites are off, usually they are not. Be very sure you need to adjust the sites first and record the small changes you make and see what changes it causes to impact.
My two cents.