Remove the Retention Module form back plate
Check the height of back plate mounting holes:

Metal Back Plate

Plastic Back Plate
If your Motherboard includes:
Metal back plate- higher mounting holes, the installation is as same as the installation guide included in "SonicTower Package"
Plastic back plate (the ASUS motherboards, for example)- lower mounting holes, the installation is as following.
 
Take the following components from the component box:
#6-32 screws x 2
washer x 2
I-bar x 1

 
Place the retention module and
back plate
 
Place a thin layer of thermal grease
 
Put the " SonicTower" cooler onto the CPU
Put the "I-bar" onto the heat sink as shown in the picture
Put the screws and washers through the mounts of I-bar and
screw evenly in each side. Complete the installation.