You have 2 bolts and one nut; the one on the top, which should you should do just a bit to release the alternator, one on the bottom, which is the one to adjust the tension, and the nut hidden on the side, which you must undo a bit so you can adjust the tension:
Take a look at the following picture:
http://www.hondaoriginalparts.com/honda_car_parts_selection_pfk.php?block_01=17S1A11&block_02=E__0601&block_03=2300
Upper bolt - nº 15
Lower bolt - nº 13
Side nut - nº 18