I orient my guitar cartons with the headstock end facing up, and place address labels on that end, which is the best position for the packing to best support a guitar; And the shipper will pack it in their shipping containers that way, address label up; Which eliminates the chance of something large and heavy being stacked on top.
To open the carton, get a pair of scissors, and razor knife or sharp knife and a garbage bag ready. Then lay the carton on a substantial and flat surface with the 'LID' facing up like shown below:
Use a razor knife to cut THE TAPE along the 3 edges marked 'CUT EDGE'. Then lift the LID to hinge on the 'HINGE EDGE', ...up, over and out of the way.
Review the previous 4 packing pages in reverse order to see how to easily unpack the guitar from it's cartons.