It is pretty easy, follow those 3 steps:
1 - Launch SongPop
2 - Go to your settings (click on the wheel icon in the upper right corner of the home page)
3 - If you are a VIP, under your profile picture, you should see a yellow ribbon with the word "VIP".
4 - If you are a Diamond VIP, under your profile picture, you should see a black ribbon with the words "Diamond VIP", and your profile will display your badges on top of your profile picture.