Lay the Dell Optiplex GX260 down on a clean flat surface with the rear towards you.
Push the oval shaped buttons located on the top and bottom of the PC simultaneously and lift the case straight up.
Disconnect the fan cable from the motherboard.
On the rear of the desktop, push the two circled black buttons straight in with a small pointed object while pulling up on the fan.
Once the fan is released, lift it straight up and out of the case.