There are two kinds of product upgrades.
Major upgrades change the whole number of the product. For example, this would be version 1.x to version 2.x. Major upgrades include a fee, usually a discount off the full price of the product.
Minor upgrades do not change the whole portion of the version number. For example, this would be version 1.1 to version 1.2. Minor upgrades are free of charge.