If it works the same way as this forum, you'll find those things in the "administration" section.
There is a list saying bans where you can add the username to ban, then hitting "ban" will give you more options such as setting an expirey date for the ban.
As to removing, to do that you need to use the search members feature in admin, find the account and remove it.
i'd recommend using ban instead of remove for spambots though, sinse banning them also banns their ip and e-mail address, meaning they can't register again with the same details.
With our dreaming and singing, Ceaseless and sorrowless we! The glory about us clinging Of the glorious futures we see,
Our souls with high music ringing; O men! It must ever be
That we dwell in our dreaming and singing, A little apart from ye. (Arthur O'Shaughnessy 1873.)