No, it should have automatically recognised the upgrade. Are the chips the same brand? Also, take out the new stick and blow the dust out of the chip socket and reseat the chip . Make sure you seat in in all the way. Im guessing the dust is making for a poor connection. While you got it open, also blow the dust out of everything while your at it. Too many people neglect cleaning..it makes a system happy (and cooler)
If you use those arosal cans that are used for cleaning computers..do NOT spray anything until the system is completly cooled down, and DONT refire the comp back up until it becomes room temperature again (the arosal is extremlely cold)