Update query with JOIN

One of my colleague just asked me about update query with JOIN but as he is new to SQL he tried to do exactly same as Select query and it was failing to execute. There is little difference when you do UPDATE query with JOIN. He was trying to execute below query and was not able to understand correct syntax of the query.

UPDATE Sales.SalesPerson AS sp

        INNER JOIN  Sales.SalesOrderHeader AS so

    ON sp.BusinessEntityID = so.SalesPersonID

       SET SalesYTD = SalesYTD + SubTotal

Where sp.SalesPersonID > 1

Below is correct syntax for running UPDATE query with JOIN:

UPDATE Sales.SalesPerson

        SET SalesYTD = SalesYTD + SubTotal

FROM Sales.SalesPerson AS sp

JOIN Sales.SalesOrderHeader AS so

    ON sp.SalesPersonID = so.SalesPersonID

Where sp.SalesPersonID > 1