The handle of the faucet is stiff and hard to operate; how can I correct this?

The issue is most likely caused by a defective/ worn out cartridge, replacing the cartridge should correct the issue.

To identify replacement cartridges, you may visit the item page by searching the model number of the faucet.
Once you reach the item page, all the replacement parts should be listed under “Replacement Parts” section by the bottom of the page.
If you are having difficulties to identify the part, please feel free to contact our support team for further instructions.

You are more than welcome to contact our product specialist at [e-mail] for additional information.