Bottom Slot RAM Upgrade. This page shows you how to upgrade the memory in the bottom slot of the iMac. handy. Though, theres some little things about the article. firstly, they say that imac maxes out at 192mb ram. this is true for some and untrue for others. i have 288mb in mine now, and its posible to upgrade that to 512. depends on the mac, the memory and some other little things. I got Kingston memory. the page is here for buying imac memory.