Hi,
You can find a very useful doc (for the first way, BEx) following this link https://www.sdn.sap.com/irj/servlet/prt/portal/prtroot/com.sapportals.km.docs/documents/a1-8-4/how to report data in alternate units of measure
Otherwise, if for you it's not necessary to have the indication of the UoM with your amount
On the other hand, you can use the update rules to convert your UoM when you load data in the infoprovider !