Trouble deleting deprecated roll-up summary fields

Hello,

We recently upgraded to the Households model and have the most recent NPSP. We have several deprecated roll-up summary fields that are counting against our precious roll-up summary limit. When I try to delete these fields, I am told I can't because they are referenced in field sets. When I go to those field sets, the fields are not in the set, but they are available to add to the set.

I tried to use the mrbelvedere tool mentioned in this article:

However, I get an error on installing the first package that says: The specified package namespace: npsp does not match the namespace for the server:

Any ideas? I'd really like to get rid of these deprecated fields, but can't seem to find a path that works.

Thanks!

Blair