No, I guess I'm confusing you.  Let's do this step by step.  But first let me explain overall, you have to return (deactivate) your 2015 license so that the 2017 license is made available.  This means that once you uninstall 2015, or lose the ability to use it because of a PC crash or an operating system upgrade, you will not be able to activate it again.  If you wish to retain the use of 2015 permanently then you have to purchase a new license instead of upgrading.  Upgrading is a replacement of one version with another.  This is why it’s also less expensive.

So the process is this if you wish to upgrade a licence:

1. You will be asked to return your 2015 licence.
2. Do not return it from Studio.  So do not deactivate Studio 2015.  You return it in your account.
3. You will see that you now have a 2017 licence in your account, but the 2015 one will not be available to you anymore.  It won't even be visible.
4. Studio 2015 will still be running and activated as if you have a valid licence.  So you can install and licence 2017 as well.  They will run together quite happily.
5. If you have to uninstall 2015, change PCs, update your operating system, or anything that requires a reinstall of the software then you will not be able to activate 2015 anymore.
6. 2017 will be fine.  But 2015 will not be available to you anymore.

Does that make more sense?

Thanks

Paul