Dell YRC3G Owner's Manual page 51

NOTE: Do not pull the connector by the cable wires. Instead, disconnect the cable by pulling the connector end.
Pulling the cable wires may loosen them from the connector.
b Unroute the fan cable [1] from the system board.
c Remove the screw [2] that secure the rear system fan to the chassis.
d Lift the fan to release it from the retention slot in the system chassis [3].
Removing and installing components 51