Do yourself a favor, when trying to loosen the top bolt, get a 17mm box end wrench and turn to lock it against the frame. Use a big pair of channel locks or pipe wrench to rotate the upper shock tube. Hope that the bolt is so rusted on that it just breaks the stud. Make sure you use some sort of never seize when putting the new shock on and use a new top locking nut. Give yourself some time and have patience. Changing these shocks is a bit of a pain in the arsh.