SML: 89 Nissan Sentra

[Ed and Helynn]

My daughter's 89 Nissan Sentra is overheating...the temperature indicator
needle goes all the way to the "H" (hot).  This happens when she is driving
and when it just idles.  Do we need to replace the thermostat?  If so, can
someone tell me where this is located on the radiator/engine??  Thank you!