A Hacksaw,,,,PLEASE,,,,this is a Nissan we are talking about,,,,put away the hacksaw for ever.
1/ Remove your back wheels
2/ There is a rubber plug on the rear discs that hides the ADJUSTERS,,,,much like a drum brake rear end on an older car,,,but it's on the front face of the disc,,,,spin the disc around till you find the adjuster,,,using a torch helps....
3/ You need a lever of sorts to click the adjuster around,,,.
If you are in any doubt,,remove your discs and have a look,,,,.
Neil.