Article in English: Frozen octopus can be thawed by sitting it in the refrigerator for roughly 24 hours.  Frozen octopus actually has an advantage over fresh octopus because the freezing process helps tenderize the meat. If you are working with fresh octopus, tenderize it first by beating it with a meat tenderizer. Before cooking frozen octopus, however, it must be completely defrosted. Use a sharp kitchen knife to cleanly slice off each tentacle at its base.  Note, however, that some recipes require you to cook the octopus whole before cutting it into pieces. Make sure that you read the instructions carefully for the recipe you plan to use before slicing up the octopus. With the octopus lying flat on your working surface, hold up one tentacle and saw it off at the base. Remove the other tentacles in the same manner. If you have kitchen shears, you can cut of the tentacles more easily with those than you can with a sharp knife. Separate the head from the middle piece and cut the head in half. The middle piece that connected the octopus tentacles to the head is hard and unpleasant, so you can discard it. The head, however, should be cooked alongside the tentacles. When working with frozen octopus, this step is not usually needed, since most frozen octopus is sold with these pieces already removed.  Even if you work with fresh octopus, you can usually ask the fishmonger to clean the octopus for you before he wraps it up for you to take home. Once you halve the head or body of the octopus, the ink sac and innards should be visible. You can cut these away and remove them with little difficulty.  The beak might still be attached to the hard middle section you discarded, in which case, no further action is needed. If the beak is attached to the body, however, you can usually push it out by squeezing the octopus gently. Once it is exposed, simply cut it out and throw it away.

Summary in Vietnamese:
Rã đông bạch tuộc. Cắt phần xúc tu ra khỏi thân. Cắt phần thân và đầu. Lấy răng bạch tuột và túi mực ra nếu cần.