SQL Server 2014 EE not using all available processors First of all let me apologize for not being clear on my requirements in my original question. I am now updating my question with my current scenario:

I have few existing SQL 2014 Enterprise Edition cluster and standalone servers in my environment. I have observed that some of them are not using all the available processors on server. For e.g. One of them is only using 40 processors out of 72 available on the server. I googled for a fix of this and came to know that it could happen when you have servers upgraded from previous Server/CAL based licensed severs(I could be wrong here as well). This limits the number of processors that you can use. 

Just to double check my existing license I ran select @@version and this shows my SQL Server is Enterprise Edition only. That means Server/CAL based. I also checked schedulers on my machine and saw that only 40 of them are online and rest of them are offline. Also, there is no affinity masking configured on the server.

Now, I want to know what options do I have to correct this issue and how to apply those changes(seeking only technical details and is not about the legality or pricing of licensing.) to fix it. 

Please let me know if you need any further details.
You need to download the right ISO/EXE from your licensing site. (Could be MSDN, for example.) The one you want is Core-based, and it'll have the right installation key embedded in it. (You may also be able to check with your license admins to get it.)

Then, you can do an edition change (Books Online). For more practical details, check out Kendra Little's post on changing editions.

For folks who stumble across this question and just wonder what's going on, Aaron Bertrand has a great blog post with more background on the 20/40-core limit.