I think the power head is clogged with pine needles. The carpet head is not picking up. How do I open it to clean it out?

Make sure you have suction at the end of the hose. If not, the clog is most likely in the hose. Detach hose from vacuum and wand. Drop a coin into one end and allow it to fall through. If it doesn't drop out, the clog is definitely in the hose. Then visually check the wands for a clog
Disassembling the power nozzle is not necessary, or recommended. First, ensure the clog is in the power nozzle. Drop a coin in the wand end and see if it falls out. If not, the clog is elsewhere. You should be able to clear the power nozzle by disconnecting the wand. Use the handle of a table knife to try to push the clog back through the power nozzle, toward the brush. If that doesn't work, try using long nosed pliers to clear the clog.