If you're signed up to the beta in the Samsung members app and you live in Korea, the update should already have hit your device for you to install - if it hasn't yet, it shouldn't be long.
Samsung is enforcing a new policy for its own Theme Store that will potentially anger lots and lots of Galaxy users, as they will be able to enjoy any given free theme for fourteen days only. The Theme Store has tons of themes to choose from, many of them being free. These notifications will come with suggestions for other themes.
This may seem confusing, but you should know that Samsung Themes offers both free and paid themes.
Samsung says they want to make sure talented theme designers get reimbursed for their work. Again, keep in mind that these are free themes. Looking at the top charts, they are unsurprisingly dominated by the free themes. There is no way for the user to purchase the theme or "unlock" a full version. The policy change will arrive alongside the Android Pie update for the respective device. Users are going to hate the change and we don't blame them. Those who don't want to stand out can also go with the more common Midnight Black or Titanium Gray, but there is also a Lilac Purple color choice.