Though Samsung claimed the change would come several days ago, the Samsung Apps store has just rebranded itself to Galaxy Apps with an update to the application. Coming with the rebrand to the "Galaxy" name is a slight change in visual styling of the app to darker shades of blue and a few new animations, though the app overall performs much the same as it did before. There's also a new app icon that comes in the shape of a slightly different shopping bag, of course.
While the move back to a Galaxy brand from Samsung is a little puzzling after Samsung spent so much time working to bring everything under one roof, from the consumer standpoint this helps with some potential confusion now that it offers both Android and Tizen devices. Since Samsung only associates the Galaxy brand with Android devices, Galaxy Apps will be the go-to place for apps on that platform.
If your device hasn't updated to replace Samsung Apps with Galaxy Apps, go ahead and open Samsung Apps and check for updates. You'll likely be prompted to download the update, then agree to some new terms of service and you'll be on your way.