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Hi there, the printer should display which colour cartridge is running low. You would only need to replace that colour. They are ordered on this page by packs (containing all 4 colours) first and then black, cyan, magenta then yellow (each also has the colour icon next to the image and how many pages it can print).
https://www.tonergiant.co.uk/model/HP-Colour-LaserJet-Pro-M254dw-toner-cartridges/
If you can let me know which colour, I can direct you to the correct product.