Upgrade from a full purchase of last major Version.
For example, if you had purchased Version 2.0 of a product at full price, then for a token $20 you may obtain the license for Version 3.0
However, minor updates are free. That is, your major license remains valid (and you do not have to pay) if you download Version 2.2 or Version 2.4 after purchasing Version 2.0. You will not have to pay full cost again till upper majoràupgrade (or above that you buy just thereafter), say Version 4.0