How do you replace the head gasket located on a 1992 Nissan Sentra?

Not really a hard proceddure. Your biggest challenge will be to reset the timing on the engine, but can be done relatively easily if done right. Simply mark timing belt, Cam gear, and top of block with a permanent marker. Good idea is to rotate engine by using a large socket on the crankshaft until timing marks line up, then mark all items (timing belt, Cam gear, and top of block) First, you've got to remove all the items connected to the head itself, (carb assembly and any other items). A good idea is to take some digital photos of the top, side and all items connected to the head so you can reference when re-assembling later. After removing all components, remove the valve cover. Once removed, you'll have to take out all the head bolts. These will be REALLY tight due to each bolt being torqued. Remove the head, use a large plastic mallet (hammer) and loosen the head by tapping on the sides. Once loose, remove the head and place on a soft surface (several layers of cardboard) Use a putty knife and remove the old head gasket. Scrape any residual oil build up or other material from head and top of engine block. Place new head gasket on the engine block in accordance with service manual or MFG recommendations. Carefully replace head on top of the head gasket and place head bolts into holes you removed them from. Tighted down with regular socket drive until nice and snug. Use torque wrench and tighten bolts using star method as indicated in service manual or ask anyone who's worked on engines to show you. Reset Cam and timing marks with marks you made and replace the timing belt. Use photos you took prior to disassembly to place all items back on the head.