The Portofino is an HX, yeah?
Adjusting the pressure stat raises and lowers the pressure that the heating element generates by raising and lowering the temperature of the water in the boiler. The two are inter-linked.
The brew temp is adjusted through flushing the HX. Usually by letting the group run until it stops sputtering/spewing boiling water, but more accurately by checking how long/much it takes to flush the group to the desired temp with an accurate TC and a decent digital thermometer.
I use a Scace Device and a Fluke 54 II that I've modified to test brew pressure as well.
I just want to echo Chris and Brady. You might not actually have a problem that requires the adjustment of the p-stat. Go through the tutorial Brady linked and get comfortable "temp-surfing" with your machine. I think you'll find that understanding the flush process on your hX machine might solve your issue.
What kind of temp problems are you having, by the way? Too low or too high? Is the machine left on all the time? Do you keep the portafilters in the groups all the time? Is the machine new? Tell us how you are using the machine and we might be able to help figure out the problem.