HP Officejet Pro X551 Printer series - Manual (Page 89)

3. Grasp the edge of the old ink cartridge and
then pull the cartridge straight out to remove it.
4. Remove the new ink cartridge from the
packaging.
5. Do not touch the metal connector of the ink
cartridge. Fingerprints on the connector can
cause print-quality problems.
ENWW Replacement instructions 75