If you already bought Version 5, this update is free.
If you are upgrading from version 4, this may be a paid upgrade for you.
If you have a Default Folder X license purchased before June 1, 2015, there is a $14.95 upgrade fee for this
version. If you purchased on or after June 1, 2015, your upgrade is free and your existing serial number will work in version 5.1.