How do you make your old profile picture your new profile picture so that you can retain the number of likes it had and so forth (so it doesn't reset to 0 likes) ?
Just go to your profile and images link. You 'll be listed with the images that you have uploaded and also other option lists you down with the profile pictures that you have used. Go and include the same. Your likes, comments everything 'll be retained.
In short: Don't upload new one, use the same one.