I have a imac as above, which has 2 x 2gb memory cards installed, I would like to upgrade my memory by putting in 4 new ones each being 4gb making a total of 16gb, but what happens to the memory already on the 2 cards in the mac, if i remove them will I loose all the stored memory in my photos, word etc. ? please help, als can I have a total of 32gb in this model?
The memory you are talking about (also called RAM) does not "store". It only "temporary" stores.
It is used for when computer is running to shuffle stuff around getting it from your hard disk (memory) and putting it back to it pending what you are doing. It does not stores anything permanently.
Your files are stored on your hard disk. So go ahead and upgrade the memory.