Peace be upon you. According to Grand Ayatollah Khamenei (may Allah protect him): If the individual has set aside the money with the intention of charity, as long as it has not been handed over, they may exchange it for another currency or convert it within the same currency, such as replacing smaller denominations with a single bill of the same value. However, if the money was collected from individuals in the community, it cannot be exchanged or spent without the donors' permission. Any individual entrusted with delivering the charity must do so as it is and cannot act with the intention of substituting it later. Source: Fiqh Al-Wali. According to Grand Ayatollah Sistani (may Allah protect him): If the charity is not specified, it can be exchanged with the owner's permission. Source: Official website. May you be successful in all good.