You can manage credits and refunds through the Credits and Refunds tabs within an account (Accounts > search for account > Aria Payments and Credits).
Removing Read/Create permission on payments and refunds disables the Payments and Refunds tabs, respectively. Allowing Read access allows you to view the payments and refunds history from the Payments and Credits tabs. Allowing both Read and Create access allows you to view and create payments and refunds from these tabs.
From Salesforce, you can create credits and issue refunds.