What is the process to upgrade an unmanaged package that is currently Installed in production?

For an unmanaged package, Salesforce documentation states that the developer who created and uploaded the package has no control over installed components and can’t change or upgrade them after installation.

Therefore, an unmanaged package does not follow the normal managed-package upgrade path. To get a newer version, the practical process is to remove the installed unmanaged package and install the newer version.

Why others are incorrect:

B and D describe managed/update-style behavior, not unmanaged package behavior.

C is not the package upgrade process itself; it describes a deployment workaround, not upgrading the installed unmanaged package.

===========