Installing fan Intel Pentium 4 540J / 3 2 GHz clientpro 365

If it has a P4 chip which I'm assuming it does from the title, then it should be the 4 pins you have to turn anti-clockwise and pull up one at a time. You may need a flat-head screwdriver for this.

Don't forget if you're removing or changing a heatsink and fan unit then it's a good idea to remove any residue left over from the previous application of thermal paste and then reapply fresh thermal paste when you install the heatsink again.