Depending on the type of InkJet you have, if the print head is a part of the ink cartridge I would not recommend refilling the cartridge, as the print head‘s life is based on the amount of ink the catridge comes with, if this is done you will usually get print quality defects. If you do decide to refill this type of cartridge, I wouldn‘t recommend doing it more then once.
If the ink and print head are separate you can usually refill them without to much trouble, much cheaper then new cartridges... In this case I would recommend reading the manual to see how many print cartridges the print head is rated at however, using refilled cartridges can decrease the life of the print head.
In any case, if you do happen to get print quality defects of any kind while using refilled cartridges, I suggest trying new catridges as your first troubleshooting step. as it will probably be the cause...