Synology RS1221+ Hardware Installation Manual page 21

b Remove the screws that secure the fan guard from the malfunctioning fan.
5 Install a new fan:
a Attach the fan guard to the new fan, then tighten the screws to secure the fan guard.
b Plug the power cord of the new fan into your Synology NAS.
6 Replace the top cover by following step 5 of the "To install the memory module" section.
7 Reconnect the cables that removed, then press the power button to turn on your Synology NAS.
21 Chapter 3: System Maintenance