.NET architects are best placed to guide the migration of legacy projects to newer versions of .NET because they have a global view of the entire project. For a successful migration, the architect should start by creating a detailed migration plan that has a list of changes to be made, framework components to be upgraded, and potential migration risks like downtimes and how to mitigate them.
For the actual migration, the architect should oversee a controlled migration following the guidelines and best practices outlined by Microsoft. Migration activities to initiate and oversee as a .NET architect include incremental refactoring, testing, compatibility tests, and framework-specific updates to ensure a smooth migration. They should also come up with a deployment plan that accommodates existing IT infrastructure or a design plan for a new one if necessary.