You would remove the 512, yes. But the thing is 4gb is wasted money unless you have a 64 bit operating system, as 32 bit systems usually don't "see" any more than 3GB. I've had trouble with more than 2GB before. Plus if you don't have a fast processor it's questionable whether 4GB of RAM will be a huge speed increase over 2GB.

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1985 CA 300D Turbo , 213K mi