Open the current reseller page or the reseller options in your account and choose a credit package. If offered, select Get This Plan, then Add Credits in the Starting out or restocking credits? checkout field to top up an existing panel. Follow the current payment instructions.
A top-up normally adds credits to the existing panel balance without resetting it. Check the actual balance after payment is confirmed and the top-up is processed. If the credits are missing, contact human support with the order number. Current quantities and prices are shown in your account, reseller page or checkout.