While you are able to edit your funding source’s name, owner, code, and currency, you are unable to edit the balance of your funding source. The balance of a funding source can only be altered by applying credit to the funding source or allocating credit from the funding source to a fund.
Select Administration → Acquisitions Administration → Funding Sources.
Make your changes and click Save.
Editing the currency of an active in use funding source is not recommended as it can have serious consequences.