In order to change the amount and/or currency that you have committed to be deposited while being on the waitlist, use the "Deposit" function to commit a new amount. The previous amount will be overwritten by the newly specified amount and currency.
You will be able to verify the updated amount and currency on the Dashboard.
Please note that if you go to "Withdrawal" and cancel your deposit commitment, you will lose your spot in the waitlist. Therefore, to preserve your spot, just overwrite your amount on the "Deposit" page.