Add, Change, or Remove a Merchant Account for Credit Card Sales

In the Home window, on the Setup menu, select Settings. Open Company, Credit Cards, and then Processing Service.
Enter the Merchant ID and Merchant Key that Sage Payment Solutions provided when you signed up for a merchant account.
Note: Sage Payment Solutions only accepts Canadian currency from Canadian merchant accounts and US currency from US merchant accounts. If you signed up for a Canadian merchant account, enter the account information in the CAD Merchant Account fields. If you signed up for a US merchant account, enter the account information in the USD Merchant Account fields.
If you accept payments made with foreign currencies, click Add Currencies and Connect Them to Your Merchant Accounts to connect a merchant account with a foreign currency so that the merchant account is automatically selected for debit and credit card payments made with this currency
Click OK.

In the Home window, on the Setup menu, select Settings. Open Company, Credit Cards, and then Processing Service.
Change the Merchant ID and Merchant Key to the new merchant account that you want to use.
Click OK.

In the Home window, on the Setup menu, select Settings. Open Company, Credit Cards, and then Processing Service.
Clear both the Merchant ID and the Merchant Key.
Click OK.