Dell Dimension C521 Owner's Manual page 70

4 If you are replacing a card that is already installed in the computer, remove the card.
If necessary, disconnect any cables connected to the card. Grasp the card by its top corners, and ease it
out of its connector.
5 Prepare the card for installation.
See the documentation that came with the card for information on configuring the card, making
internal connections, or otherwise customizing it for your computer.
CAUTION:
Some network adapters automatically start the computer when they are connected to a network. To
guard against electrical shock, be sure to unplug your computer from its electrical outlet before installing any
cards.
6 Place the card in the connector and press down firmly. Ensure that the card is fully seated in the slot.
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Removing and Installing Parts
1 release tab 2 card retention door
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2