Re: How do I change my existing campaign type to shopping?
It looks like you are asking about upgrading from PLA to Shopping campaigns here. Let me know if that's not the case here.
Here's the upgrade guide which will help you do that: http://services.google.com/fh/files/misc/shoppingcampaigns-upgradeguide.pdf
This is the help center detailed reference for more insights: https://support.google.com/adwords/answer/4637089?hl=en
Hope this helps!