Apple iMac (Early 2009) - Manual (Page 33)

Chapter 3 Boost Your Memory 33
Installing Memory
Your iMac has two memory slots, each filled with at least a 1 GB memory module.
You can replace the memory module in either slot with 2 GB or 4 GB memory modules
for up to 8 GB of memory.
You can purchase additional Apple memory from an Apple Authorized Reseller,
an Apple Store retail location, or the online Apple Store at www.apple.com/store.
To install memory
1 Turn your iMac off by choosing Apple () > Shut Down.
2 Disconnect all cables and the power cord from your iMac.
3 Place a soft, clean towel or cloth on your work surface. Hold the sides of your iMac and
lay it down so that the screen is against the surface and the bottom is facing you.
WARNING: Always shut down your iMac and remove the power cord before installing
memory. Do not attempt to install memory while your iMac is plugged in.