The first you have to do before installation is to get the mounting clip into the heatsink.
Sliding it in is a little bit tricky because the white plastic part is higher than the opening at the bottom of the heatsink. With a little bit clever moving it is no problem though.
Installation of the cooler is very easy.
You hook in the clip on the side without the lever.
Hook it in on the other side and turn down the lever.
Since the heatsink is fixed only in the center it can be rotated slightly. This allows you to optimize the airflow to go over the memory or to the video card for example.
You can install a 92mm fan of your choice to the Ultra 90. Installation is very straightforward. You use the included clips to fix the fan to the heatsink assembly. This is easy to do and can be done multiple times without the clips ever bending.
To verify that the fan has a tight connection to the heatsink I hung the whole heatsink from the fan cable only. It was rock solid as you can see.