via EuroDNS control panel
Log in to your EuroDNS account, click on Control Panel.
Click on the Account Details in the upper left corner. Renewal Method is bottom right, take your pick!
via WHMCS admin panel
Log in to your WHMCS admin panel. Click on the column Setup and select General Settings.
Click on the Domain dropdown menu. You’ll find your choices at the top of the page
You can set the renewal method in either WHMCS or your EuroDNS account. Your setting will be changed in both platforms.