You can certainly change your music album cover! However, you can only select a cover image from the list of pictures «built into» the songs included in the album. To change the main photo of your music collection:

• Go to the «Music» section;
• Go to the menu on the left and open the «My music» tab;
• Open the corresponding collection (please note that it must be created by you, not added from another user's profile or catalog);
• Click «More» – «Edit» under the album cover;
• Next, just click the arrows that appear on the collection cover until you find an option you like, or click the camera icon on the image to upload a new picture from your PC;
• Then just check the box to the right of the collection name.