Q:

API Endpoint Change Effective 1/1/2016 Salesforce

I received notice of API endpoint change effective 1/1/2016. How can I know if this would affect me and what is the best way to know what all changes I have to make in my Salesforce.
So lets say I have hardcoded this www.salesforce.com in plenty of times within my code, do I need to change it everywhere manually or is there a better way?
Any help would be much appreciated !!!

Knowledge Article www.salesforce.com API Endpoint Retirement
Text from the www.salesforce.com API endpoint will be retired January 1 email.

Product & Service Notification
As an admin of a Salesforce org, we want to notify you of an important change to the availability and support of www.salesforce.com as an API endpoint. 
What is changing?
  Currently, customers can use www.salesforce.com as an API endpoint that will route them to the correct instance. As of January 1, 2016, the internal routing will be retired, and any API endpoints will need to be changed if from www.salesforce.com to https://login.salesforce.com. 
Note: This only applies to API traffic; logging in from a browser by clicking “login” will still work.
Why are we retiring the internal routing?
  This change is to ensure we focus our development efforts on delivering better performance and higher availability on the dedicated API endpoints.
What action do I need to take?
  Update your integrations to replace www.salesforce.com with https://login.salesforce.com, as the official endpoint for the Salesforce API. 
Please see the Best Practices When Referencing Server Endpoints article.
What will happen if I do not take action?
  The API will no longer function, and your API calls will result in a “404 (Page Not Found)” error.
How can I get more information?
  For additional questions, you can open a case with Customer Support via the Help & Training portal.
For an overview of our philosophy on retiring functionality, please click here.
Any unreleased services or features referenced in this or other press releases or public statements are not currently available and may not be delivered on time or at all. Customers who purchase Salesforce applications should make their purchase decisions based upon features that are currently available. 

A:

Short Answer
If you're not sure then search for "www.salesforce.com" and see what you find. If you find it, replace it.
Longer Answer
This is primarily a warning for those integrating with Salesforce, so yes, if you have code that's referencing www.salesforce.com as part of an authentication request for example, then you would need to change your code and correctly choose test.salesforce.com or login.salesforce.com based on whether the user is trying to log in to a sandbox or other org.
If your only code is in Apex, then I highly doubt you have any references, and chances are if you've used any of the official SDKs from the last 5 years you wouldn't do so either.
As for having to replace it that would depend on your IDE or similar. Most tools offer a global search and replace, or you could use a command-line utility such as sed. 

