Members List?

[Togashi]

I don't know what version you are running, but from google:

Yes, in admincp under the user tab, select users and at the bottom left there is a drop down option, select delete or prune and hit go.

Only the board administrator may be able to perform the action.

I would also suggest deleting forums that no one has responded to in months, maybe moving them to an archived section in case people still want things from them.