Hi,
When you add one or several characteristics to a product, HikaShop creates one variant of that product per combination of values of the characteristics. That way, you have the possibility, via the "manage variants" button, to set different prices for each variant, or manage your stocks on a per variant basis.
Now, if you change the values of the characteristics after that, the variants of your products are still there with the old values.
So, to fix that, here is want you can do:
Go in your product and click on the manage variants button. There, delete all the variants of your product. Then, go back to the product and delete the characteristic and save your product. Then, add back your characteristic and save. That way, HikaShop will recreate the variants for your product with the new values automatically.