▼For Character Skins
From the title screen (where the two "Sonic" and "Shadow" are displayed in the center), proceed to the screen where you can select "Sonic Generations" and "Shadow Generations".
In the bottom left corner of the screen, you will see the "Additional Content" option, so press the corresponding button to each model.
This will take you to the "Additional Content" screen, where you can connfigure the character skins.
▼ For additional BGM
Start "Shadow Generations" and enter the "White Space" where the Act stage gates are located.
Open the pause menu and select "Collection Room". When you approach the object that looks like a speaker inside the Collection Room, a speech bubble labled "Sound" will appear.
Press the button corresponding to each model.
If you hold the rights to additional BGM, the tracks will be available starting from the "41st song" on the displayed song list.
▼For the bonus skill points
As for the bonus skill points that can be used in “Sonic Generations”, if you start a "New Game" while holding the DLC rights, you will receive an additional "10,000" points at the beginning of the game.