I am helping a friend switch hosting provider. He bought the domain through GoDaddy and currently hosts the site at http://www.wix.com/. Where do I need to update the ip address so that the domain now points to the new hosting provider (winhost).
Your new service provider(wix.com) should give you their nameservers value.
You need to log in your Godaddy Control Panel> Domain Manager> Launch Domains>Click on Your Domain> Manage DNS> Edit Nameservers.
Look here for more information Godaddy -Setting Nameservers for a Domain Name Registered with Us
Keep in mind that after setting Wix nameservers, all the DNS records(A, MX, TXT etc) will be hosted at your wix.com account..
You need to update your DNS records, namely the A record (assuming you're not moving the email, if so, you need to point the MX record at your new IP as well).
You can find more details (specific for GoDaddy) here http://support.godaddy.com/help/article/680/managing-dns-for-your-domain-names and assumes you're still using the nameservers on the GoDaddy server.