How does one get rid of usury accrued from forex trading? Is it through charity, or by withdrawing the usurious money and donating it, or by giving charity from one's own money equal to the same value? Is it permissible to keep the "bonus," or must its value be donated?

You must immediately cease engaging in usurious transactions and repent to Allah for them. Dispose of the illicit gains and profits by spending them on Muslim welfare projects or giving them to the poor and needy. It is sufficient to disburse the same forbidden amount from any money the person owns, while also withdrawing the money from the usurious account with the company.