In this video from Tiffany0x we learn how to change your profile background on youtube. First she goes to google, then clicks on images and type in whatever image you're looking for for your background. Then copy the image's link in your browser. Then go to youtube. Click My Account. Then you'll see Channel Settings. Click that, then click Channel design. In Advanced Customizations you'll see a place where you can put in a Background URL. Paste the URL into that box. Once you have done that, click Update Channel. It should say Your Channel Has Been Updated. Then you can view your channel with your new background image!