Angel food cake is a very different type of cake from a standard vanilla sponge cake it's mostly egg whites and sugar, other cakes have more flour, so if you want to try and modify it I'd be thinking more flour and maybe some butter.
If it was me I wouldn't bother though. It may be possible to modify the mix, but you'd have to reverse engineer the recipe from the box ingredients for both mixes, then work out the quantities to make one into the other. That is making big assumptions, and it's unlikely you'll get a good result without a lot of trial and error. It's a lot of work for little return when you can just go buy another box that you do like - enough work that you may as well make a cake from scratch rather than using a mix in the first place.