How to remove the Readynas Pro CPUfan

Hello,

I asked if it was possible to remove the HDD from a broken Readynas Ultra6 and transfer it to a new Readynas.
I was unable to get a used Readynas, but finally was able to get a used Readynas Pro, so I tried it and it worked.

However, there is a new problem.

The CPU fan of this used Readynas Pro is unusually noisy.
I want to replace the CPU fan with a new one, but I don't know how to remove the fan from the heatsink.

I observed the CPU heatsink.
It seems that the fan and heatsink are held together by a U-shaped plastic hook. Can I lift up this plastic and remove the fan?

I am worried that the hooks might break if I do it forcefully.