Apple iMac 24-inch (late 2006) VESA Mount Adapter - Manual (Page 6)

6 English
6 Use the TORX tool to remove the 8 screws that attach the stand to the back of your
iMac. You’ll need these screws to attach the flange to your iMac, so set them aside.
7 Remove the stand and put it in a safe place in case you want to reattach it.
TORX tool Hex tool
TORX tool