This pic is for a shirt print gift and I'm trying to figutre out how I could make the backroung white in Adobe Photoshop CC. The effect looks fairly complex so I've no idea how to go around it, only way I think this is possible is by reproducing the effect, which I also don't know how to do.
You need to use whatever selection methods you're most comfortable with to select the cat, book, and text. Invert that selection and fill with your new color (on a new layer). Then use blending options to bring back the purple glow.
This was cropped in about 20 seconds using the Polygonal Lasso. If you take your time the Polygonal Lasso tool will be your best bet here as a beginner trying to get this done. I used it for years before ever touching Pen Tool. If you do have some experience with Pen Tool though it'll work even better. The text I just used Magic Wand.