I needed more RAM as CS5 really was slowing down.

Point is my 4GB RAM in my iMac eventually failed some functions with the error message.

"Insufficient RAM"

My computer store said the iMac was not easily upgradable.
But thanks to youtube I took the plunge.

OWC sells third party RAM and has excellent instructional videos on how to do this for many models of MAC going back to 2007.

I bought 16GB RAM for about $109 and installed it in under 10 minutes.
No problems no complications.

Now I am speeding at 16GB and RAM and can use 'photomerge' in CS5 on 8 images (have not tested more) and can use 'content aware' fill on large areas with no error messages.

Recommendations:

Updating Apple iMac RAM is EASY