Lenovo IdeaCentre K4 Series Hardware Maintenance Manual page 38

b. Remove the screw that secures the graphics card latch to the chassis, open it, and remove
the Duo-graphics cards connector.
c. Remove the graphics card by pulling it straight out of the connector.
If your computer has a single graphics card installed, follow the steps below to replace it:
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IdeaCentre K4 SeriesHardware Maintenance Manual