First, a little background.
Currently namespaces and assemblies in our codebase (~60 assemblies, thousands of classes) looks like
WidgetCompany.Depar
Firstly I would try Refactor->Rename
option. But as mentioned in comment for another answers it doesn't work that good (Or I haven't found how to make it working). So I prefer using following scenario, especially if you want to add some addiotional namespace.
1) Rename your root namespace (WidgetCompany
) to something like NAMESPACE_TO_BE_REPLACED
using Refactor-Rename
2) Replace NAMESPACE_TO_BE_REPLACED
with your final namespace (NewCompany.WidgetSoftware
) using find-n-replace dialog
And do not forget to rename projects, default namespaces, etc.