Whenever I learn to change someone shifting, I always choose Rick Mooney's phenomenal book Position pieces. It has the necessary structure, the pieces easy to predict which helps a lot to find the correct note/sound, and he is the only one from the whole methodical spectrum who offers exercises that make your brain crack about what's on each string on each finger for note in that new position. That's the essence; you can't get around it. There are 7 chapters in which he deals with the first four positions, he counts in 'lower' and 'upper' positions, and there is one last chapter in which he goes through all the positions, combining all the learned ones. Find cello structure, find it here. With all the pieces you will find a short comment by me, cello teacher for 25 years now, that tells you what I often encounter during class, what you may pay attention to to succeed asquick as possible. Good luck!