What steps should I take to remove money that I have acquired, knowingly or unknowingly, that I later discovered to be Haram, in order to ensure my remaining earnings are Halal?
Haraam (unlawful) money must be given back to its real owners, and if you don't know them or their families, then it must be given to the Marje' of Taqleed as Majhool al-Malik (unknown owner) so that he distributes it among poor believers.
If you don't know the exact amount of the unlawful money mixed with your money, you must pay an amount which makes you sure that unlawful money has been removed away from your money. That amount should be given to the Marje' of Taqleed as well so that he distributes it among poor believers.
You are not allowed to give unlawful money to charity because it does not belong to you. Allah Says in Quran ( And never deal with the unlawful by spending from it in charity, because you don't own it). (Sura al-Baqara m verse 267).
Wassalam.