the Tensioner design has been changed twice, early ones you could lock off with the thin pin in the locking kit , later ones you use an allen key /hex key to slacken the belt .
the aux belt tensioner can be locked off with the pin from the locking kit
IF you checked to see the kit is the same as fitted ,correct belt etc
and IF you have all the locking tools in place and the engine is timed and locked
just remove the belt idol pulley bolt and belt will come off
if you purchased a Gates kit as per my link then there is full instructions sheet in the box
and remember to hold the crankshaft pulley/harmonic damper onto the keyway and hand tighten the new bolt to ensure it sits correctly BEFORE torque it up or put an impact on it
and once the new belt is on and and under tension, remove ALL the locking tools (put them back in the box and make sure non are missing) BEFORE rotating the engine by hand a few times to check timing